import os
from collections import OrderedDict
from os.path import join as pjoin, dirname
from glob import glob
from io import BytesIO
import re
from tempfile import mkdtemp

import warnings
import shutil
import gzip

from numpy.testing import (assert_array_equal, assert_array_almost_equal,
                           assert_equal, assert_, assert_warns, assert_allclose)
import pytest
from pytest import raises as assert_raises

import numpy as np
from numpy import array
from scipy.sparse import issparse, eye_array, coo_array, csc_array

import scipy.io
from scipy.io.matlab import MatlabOpaque, MatlabFunction, MatlabObject
import scipy.io.matlab._byteordercodes as boc
from scipy.io.matlab._miobase import (matdims, MatWriteError, MatReadError,
                                      matfile_version, MatWriteWarning)
from scipy.io.matlab._mio import mat_reader_factory, loadmat, savemat, whosmat
from scipy.io.matlab._mio5 import (
    MatFile5Writer, MatFile5Reader, varmats_from_mat, to_writeable,
    EmptyStructMarker)
import scipy.io.matlab._mio5_params as mio5p


test_data_path = pjoin(dirname(__file__), 'data')
pytestmark = pytest.mark.thread_unsafe


def mlarr(*args, **kwargs):
    """Convenience function to return matlab-compatible 2-D array."""
    arr = np.array(*args, **kwargs)
    arr.shape = matdims(arr)
    return arr


# Define cases to test
theta = np.pi/4*np.arange(9,dtype=float).reshape(1,9)
case_table4 = [
    {'name': 'double',
     'classes': {'testdouble': 'double'},
     'expected': {'testdouble': theta}
     }]
case_table4.append(
    {'name': 'string',
     'classes': {'teststring': 'char'},
     'expected': {'teststring':
                  array(['"Do nine men interpret?" "Nine men," I nod.'])}
     })
case_table4.append(
    {'name': 'complex',
     'classes': {'testcomplex': 'double'},
     'expected': {'testcomplex': np.cos(theta) + 1j*np.sin(theta)}
     })
A = np.zeros((3,5))
A[0] = list(range(1,6))
A[:,0] = list(range(1,4))
case_table4.append(
    {'name': 'matrix',
     'classes': {'testmatrix': 'double'},
     'expected': {'testmatrix': A},
     })
case_table4.append(
    {'name': 'sparse',
     'classes': {'testsparse': 'sparse'},
     'expected': {'testsparse': coo_array(A)},
     })
B = A.astype(complex)
B[0,0] += 1j
case_table4.append(
    {'name': 'sparsecomplex',
     'classes': {'testsparsecomplex': 'sparse'},
     'expected': {'testsparsecomplex': coo_array(B)},
     })
case_table4.append(
    {'name': 'multi',
     'classes': {'theta': 'double', 'a': 'double'},
     'expected': {'theta': theta, 'a': A},
     })
case_table4.append(
    {'name': 'minus',
     'classes': {'testminus': 'double'},
     'expected': {'testminus': mlarr(-1)},
     })
case_table4.append(
    {'name': 'onechar',
     'classes': {'testonechar': 'char'},
     'expected': {'testonechar': array(['r'])},
     })
# Cell arrays stored as object arrays
CA = mlarr((  # tuple for object array creation
        [],
        mlarr([1]),
        mlarr([[1,2]]),
        mlarr([[1,2,3]])), dtype=object).reshape(1,-1)
CA[0,0] = array(
    ['This cell contains this string and 3 arrays of increasing length'])
case_table5 = [
    {'name': 'cell',
     'classes': {'testcell': 'cell'},
     'expected': {'testcell': CA}}]
CAE = mlarr((  # tuple for object array creation
    mlarr(1),
    mlarr(2),
    mlarr([]),
    mlarr([]),
    mlarr(3)), dtype=object).reshape(1,-1)
objarr = np.empty((1,1),dtype=object)
objarr[0,0] = mlarr(1)
case_table5.append(
    {'name': 'scalarcell',
     'classes': {'testscalarcell': 'cell'},
     'expected': {'testscalarcell': objarr}
     })
case_table5.append(
    {'name': 'emptycell',
     'classes': {'testemptycell': 'cell'},
     'expected': {'testemptycell': CAE}})
case_table5.append(
    {'name': 'stringarray',
     'classes': {'teststringarray': 'char'},
     'expected': {'teststringarray': array(
    ['one  ', 'two  ', 'three'])},
     })
case_table5.append(
    {'name': '3dmatrix',
     'classes': {'test3dmatrix': 'double'},
     'expected': {
    'test3dmatrix': np.transpose(np.reshape(list(range(1,25)), (4,3,2)))}
     })
st_sub_arr = array([np.sqrt(2),np.exp(1),np.pi]).reshape(1,3)
dtype = [(n, object) for n in ['stringfield', 'doublefield', 'complexfield']]
st1 = np.zeros((1,1), dtype)
st1['stringfield'][0,0] = array(['Rats live on no evil star.'])
st1['doublefield'][0,0] = st_sub_arr
st1['complexfield'][0,0] = st_sub_arr * (1 + 1j)
case_table5.append(
    {'name': 'struct',
     'classes': {'teststruct': 'struct'},
     'expected': {'teststruct': st1}
     })
CN = np.zeros((1,2), dtype=object)
CN[0,0] = mlarr(1)
CN[0,1] = np.zeros((1,3), dtype=object)
CN[0,1][0,0] = mlarr(2, dtype=np.uint8)
CN[0,1][0,1] = mlarr([[3]], dtype=np.uint8)
CN[0,1][0,2] = np.zeros((1,2), dtype=object)
CN[0,1][0,2][0,0] = mlarr(4, dtype=np.uint8)
CN[0,1][0,2][0,1] = mlarr(5, dtype=np.uint8)
case_table5.append(
    {'name': 'cellnest',
     'classes': {'testcellnest': 'cell'},
     'expected': {'testcellnest': CN},
     })
st2 = np.empty((1,1), dtype=[(n, object) for n in ['one', 'two']])
st2[0,0]['one'] = mlarr(1)
st2[0,0]['two'] = np.empty((1,1), dtype=[('three', object)])
st2[0,0]['two'][0,0]['three'] = array(['number 3'])
case_table5.append(
    {'name': 'structnest',
     'classes': {'teststructnest': 'struct'},
     'expected': {'teststructnest': st2}
     })
a = np.empty((1,2), dtype=[(n, object) for n in ['one', 'two']])
a[0,0]['one'] = mlarr(1)
a[0,0]['two'] = mlarr(2)
a[0,1]['one'] = array(['number 1'])
a[0,1]['two'] = array(['number 2'])
case_table5.append(
    {'name': 'structarr',
     'classes': {'teststructarr': 'struct'},
     'expected': {'teststructarr': a}
     })
ODT = np.dtype([(n, object) for n in
                 ['expr', 'inputExpr', 'args',
                  'isEmpty', 'numArgs', 'version']])
MO = MatlabObject(np.zeros((1,1), dtype=ODT), 'inline')
m0 = MO[0,0]
m0['expr'] = array(['x'])
m0['inputExpr'] = array([' x = INLINE_INPUTS_{1};'])
m0['args'] = array(['x'])
m0['isEmpty'] = mlarr(0)
m0['numArgs'] = mlarr(1)
m0['version'] = mlarr(1)
case_table5.append(
    {'name': 'object',
     'classes': {'testobject': 'object'},
     'expected': {'testobject': MO}
     })
fp_u_str = open(pjoin(test_data_path, 'japanese_utf8.txt'), 'rb')
u_str = fp_u_str.read().decode('utf-8')
fp_u_str.close()
case_table5.append(
    {'name': 'unicode',
     'classes': {'testunicode': 'char'},
    'expected': {'testunicode': array([u_str])}
     })
case_table5.append(
    {'name': 'sparse',
     'classes': {'testsparse': 'sparse'},
     'expected': {'testsparse': coo_array(A)},
     })
case_table5.append(
    {'name': 'sparsecomplex',
     'classes': {'testsparsecomplex': 'sparse'},
     'expected': {'testsparsecomplex': coo_array(B)},
     })
case_table5.append(
    {'name': 'bool',
     'classes': {'testbools': 'logical'},
     'expected': {'testbools':
                  array([[True], [False]])},
     })

case_table5_rt = case_table5[:]
# Inline functions can't be concatenated in matlab, so RT only
case_table5_rt.append(
    {'name': 'objectarray',
     'classes': {'testobjectarray': 'object'},
     'expected': {'testobjectarray': np.repeat(MO, 2).reshape(1,2)}})


def types_compatible(var1, var2):
    """Check if types are same or compatible.

    0-D numpy scalars are compatible with bare python scalars.
    """
    type1 = type(var1)
    type2 = type(var2)
    if type1 is type2:
        return True
    if type1 is np.ndarray and var1.shape == ():
        return type(var1.item()) is type2
    if type2 is np.ndarray and var2.shape == ():
        return type(var2.item()) is type1
    return False


def _check_level(label, expected, actual):
    """ Check one level of a potentially nested array """
    if issparse(expected):  # allow different types of sparse matrices
        assert_(issparse(actual))
        assert_array_almost_equal(actual.toarray(),
                                  expected.toarray(),
                                  err_msg=label,
                                  decimal=5)
        return
    # Check types are as expected
    assert_(types_compatible(expected, actual),
            f"Expected type {type(expected)}, got {type(actual)} at {label}")
    # A field in a record array may not be an ndarray
    # A scalar from a record array will be type np.void
    if not isinstance(expected, np.void | np.ndarray | MatlabObject):
        assert_equal(expected, actual)
        return
    # This is an ndarray-like thing
    assert_(expected.shape == actual.shape,
            msg=f'Expected shape {expected.shape}, got {actual.shape} at {label}')
    ex_dtype = expected.dtype
    if ex_dtype.hasobject:  # array of objects
        if isinstance(expected, MatlabObject):
            assert_equal(expected.classname, actual.classname)
        for i, ev in enumerate(expected):
            level_label = f"{label}, [{i}], "
            _check_level(level_label, ev, actual[i])
        return
    if ex_dtype.fields:  # probably recarray
        for fn in ex_dtype.fields:
            level_label = f"{label}, field {fn}, "
            _check_level(level_label,
                         expected[fn], actual[fn])
        return
    if ex_dtype.type in (str,  # string or bool
                         np.str_,
                         np.bool_):
        assert_equal(actual, expected, err_msg=label)
        return
    # Something numeric
    assert_array_almost_equal(actual, expected, err_msg=label, decimal=5)


def _load_check_case(name, files, case):
    for file_name in files:
        matdict = loadmat(file_name, struct_as_record=True, spmatrix=False)
        label = f"test {name}; file {file_name}"
        for k, expected in case.items():
            k_label = f"{label}, variable {k}"
            assert_(k in matdict, f"Missing key at {k_label}")
            _check_level(k_label, expected, matdict[k])


def _whos_check_case(name, files, case, classes):
    for file_name in files:
        label = f"test {name}; file {file_name}"

        whos = whosmat(file_name)

        expected_whos = [
            (k, expected.shape, classes[k]) for k, expected in case.items()]

        whos.sort()
        expected_whos.sort()
        assert_equal(whos, expected_whos,
                     f"{label}: {whos!r} != {expected_whos!r}"
                     )


# Round trip tests
def _rt_check_case(name, expected, format):
    mat_stream = BytesIO()
    savemat(mat_stream, expected, format=format)
    mat_stream.seek(0)
    _load_check_case(name, [mat_stream], expected)


# generator for tests
def _cases(version, filt='test%(name)s_*.mat'):
    if version == '4':
        cases = case_table4
    elif version == '5':
        cases = case_table5
    else:
        assert version == '5_rt'
        cases = case_table5_rt
    for case in cases:
        name = case['name']
        expected = case['expected']
        if filt is None:
            files = None
        else:
            use_filt = pjoin(test_data_path, filt % dict(name=name))
            files = glob(use_filt)
            assert len(files) > 0, \
                f"No files for test {name} using filter {filt}"
        classes = case['classes']
        yield name, files, expected, classes


@pytest.mark.parametrize('version', ('4', '5'))
def test_load(version):
    for case in _cases(version):
        _load_check_case(*case[:3])


@pytest.mark.parametrize('version', ('4', '5'))
def test_whos(version):
    for case in _cases(version):
        _whos_check_case(*case)


# generator for round trip tests
@pytest.mark.parametrize('version, fmts', [
    ('4', ['4', '5']),
    ('5_rt', ['5']),
])
def test_round_trip(version, fmts):
    for case in _cases(version, filt=None):
        for fmt in fmts:
            _rt_check_case(case[0], case[2], fmt)


def test_gzip_simple():
    xdense = np.zeros((20,20))
    xdense[2,3] = 2.3
    xdense[4,5] = 4.5
    x = csc_array(xdense)

    name = 'gzip_test'
    expected = {'x':x}
    format = '4'

    tmpdir = mkdtemp()
    try:
        fname = pjoin(tmpdir,name)
        mat_stream = gzip.open(fname, mode='wb')
        savemat(mat_stream, expected, format=format)
        mat_stream.close()

        mat_stream = gzip.open(fname, mode='rb')
        actual = loadmat(mat_stream, struct_as_record=True, spmatrix=False)
        mat_stream.close()
    finally:
        shutil.rmtree(tmpdir)

    assert_array_almost_equal(actual['x'].toarray(),
                              expected['x'].toarray(),
                              err_msg=repr(actual))


def test_multiple_open():
    # Ticket #1039, on Windows: check that files are not left open
    tmpdir = mkdtemp()
    try:
        x = dict(x=np.zeros((2, 2)))

        fname = pjoin(tmpdir, "a.mat")

        # Check that file is not left open
        savemat(fname, x)
        os.unlink(fname)
        savemat(fname, x)
        loadmat(fname)
        os.unlink(fname)

        # Check that stream is left open
        f = open(fname, 'wb')
        savemat(f, x)
        f.seek(0)
        f.close()

        f = open(fname, 'rb')
        loadmat(f)
        f.seek(0)
        f.close()
    finally:
        shutil.rmtree(tmpdir)


def test_mat73():
    # Check any hdf5 files raise an error
    filenames = glob(
        pjoin(test_data_path, 'testhdf5*.mat'))
    assert_(len(filenames) > 0)
    for filename in filenames:
        fp = open(filename, 'rb')
        assert_raises(NotImplementedError,
                      loadmat,
                      fp,
                      struct_as_record=True)
        fp.close()


def test_warnings():
    # This test is an echo of the previous behavior, which was to raise a
    # warning if the user triggered a search for mat files on the Python system
    # path. We can remove the test in the next version after upcoming (0.13).
    fname = pjoin(test_data_path, 'testdouble_7.1_GLNX86.mat')
    with warnings.catch_warnings():
        warnings.simplefilter('error')
        # This should not generate a warning
        loadmat(fname, struct_as_record=True)
        # This neither
        loadmat(fname, struct_as_record=False)


def test_regression_653():
    # Saving a dictionary with only invalid keys used to raise an error. Now we
    # save this as an empty struct in matlab space.
    sio = BytesIO()
    savemat(sio, {'d':{1:2}}, format='5')
    back = loadmat(sio)['d']
    # Check we got an empty struct equivalent
    assert_equal(back.shape, (1,1))
    assert_equal(back.dtype, np.dtype(object))
    assert_(back[0,0] is None)


def test_structname_len():
    # Test limit for length of field names in structs
    lim = 31
    fldname = 'a' * lim
    st1 = np.zeros((1,1), dtype=[(fldname, object)])
    savemat(BytesIO(), {'longstruct': st1}, format='5')
    fldname = 'a' * (lim+1)
    st1 = np.zeros((1,1), dtype=[(fldname, object)])
    assert_raises(ValueError, savemat, BytesIO(),
                  {'longstruct': st1}, format='5')


def test_4_and_long_field_names_incompatible():
    # Long field names option not supported in 4
    my_struct = np.zeros((1,1),dtype=[('my_fieldname',object)])
    assert_raises(ValueError, savemat, BytesIO(),
                  {'my_struct':my_struct}, format='4', long_field_names=True)


def test_long_field_names():
    # Test limit for length of field names in structs
    lim = 63
    fldname = 'a' * lim
    st1 = np.zeros((1,1), dtype=[(fldname, object)])
    savemat(BytesIO(), {'longstruct': st1}, format='5',long_field_names=True)
    fldname = 'a' * (lim+1)
    st1 = np.zeros((1,1), dtype=[(fldname, object)])
    assert_raises(ValueError, savemat, BytesIO(),
                  {'longstruct': st1}, format='5',long_field_names=True)


def test_long_field_names_in_struct():
    # Regression test - long_field_names was erased if you passed a struct
    # within a struct
    lim = 63
    fldname = 'a' * lim
    cell = np.ndarray((1,2),dtype=object)
    st1 = np.zeros((1,1), dtype=[(fldname, object)])
    cell[0,0] = st1
    cell[0,1] = st1
    savemat(BytesIO(), {'longstruct': cell}, format='5',long_field_names=True)
    #
    # Check to make sure it fails with long field names off
    #
    assert_raises(ValueError, savemat, BytesIO(),
                  {'longstruct': cell}, format='5', long_field_names=False)


def test_cell_with_one_thing_in_it():
    # Regression test - make a cell array that's 1 x 2 and put two
    # strings in it. It works. Make a cell array that's 1 x 1 and put
    # a string in it. It should work but, in the old days, it didn't.
    cells = np.ndarray((1,2),dtype=object)
    cells[0,0] = 'Hello'
    cells[0,1] = 'World'
    savemat(BytesIO(), {'x': cells}, format='5')

    cells = np.ndarray((1,1),dtype=object)
    cells[0,0] = 'Hello, world'
    savemat(BytesIO(), {'x': cells}, format='5')


def test_writer_properties():
    # Tests getting, setting of properties of matrix writer
    mfw = MatFile5Writer(BytesIO())
    assert_equal(mfw.global_vars, [])
    mfw.global_vars = ['avar']
    assert_equal(mfw.global_vars, ['avar'])
    assert_equal(mfw.unicode_strings, False)
    mfw.unicode_strings = True
    assert_equal(mfw.unicode_strings, True)
    assert_equal(mfw.long_field_names, False)
    mfw.long_field_names = True
    assert_equal(mfw.long_field_names, True)


def test_use_small_element():
    # Test whether we're using small data element or not
    sio = BytesIO()
    wtr = MatFile5Writer(sio)
    # First check size for no sde for name
    arr = np.zeros(10)
    wtr.put_variables({'aaaaa': arr})
    w_sz = len(sio.getvalue())
    # Check small name results in largish difference in size
    sio.truncate(0)
    sio.seek(0)
    wtr.put_variables({'aaaa': arr})
    assert_(w_sz - len(sio.getvalue()) > 4)
    # Whereas increasing name size makes less difference
    sio.truncate(0)
    sio.seek(0)
    wtr.put_variables({'aaaaaa': arr})
    assert_(len(sio.getvalue()) - w_sz < 4)


def test_save_dict():
    # Test that both dict and OrderedDict can be saved (as recarray),
    # loaded as matstruct, and preserve order
    ab_exp = np.array([[(1, 2)]], dtype=[('a', object), ('b', object)])
    for dict_type in (dict, OrderedDict):
        # Initialize with tuples to keep order
        d = dict_type([('a', 1), ('b', 2)])
        stream = BytesIO()
        savemat(stream, {'dict': d})
        stream.seek(0)
        vals = loadmat(stream)['dict']
        assert_equal(vals.dtype.names, ('a', 'b'))
        assert_array_equal(vals, ab_exp)


def test_1d_shape():
    # New 5 behavior is 1D -> row vector
    arr = np.arange(5)
    for format in ('4', '5'):
        # Column is the default
        stream = BytesIO()
        savemat(stream, {'oned': arr}, format=format)
        vals = loadmat(stream)
        assert_equal(vals['oned'].shape, (1, 5))
        # can be explicitly 'column' for oned_as
        stream = BytesIO()
        savemat(stream, {'oned':arr},
                format=format,
                oned_as='column')
        vals = loadmat(stream)
        assert_equal(vals['oned'].shape, (5,1))
        # but different from 'row'
        stream = BytesIO()
        savemat(stream, {'oned':arr},
                format=format,
                oned_as='row')
        vals = loadmat(stream)
        assert_equal(vals['oned'].shape, (1,5))


def test_compression():
    arr = np.zeros(100).reshape((5,20))
    arr[2,10] = 1
    stream = BytesIO()
    savemat(stream, {'arr':arr})
    raw_len = len(stream.getvalue())
    vals = loadmat(stream)
    assert_array_equal(vals['arr'], arr)
    stream = BytesIO()
    savemat(stream, {'arr':arr}, do_compression=True)
    compressed_len = len(stream.getvalue())
    vals = loadmat(stream)
    assert_array_equal(vals['arr'], arr)
    assert_(raw_len > compressed_len)
    # Concatenate, test later
    arr2 = arr.copy()
    arr2[0,0] = 1
    stream = BytesIO()
    savemat(stream, {'arr':arr, 'arr2':arr2}, do_compression=False)
    vals = loadmat(stream)
    assert_array_equal(vals['arr2'], arr2)
    stream = BytesIO()
    savemat(stream, {'arr':arr, 'arr2':arr2}, do_compression=True)
    vals = loadmat(stream)
    assert_array_equal(vals['arr2'], arr2)


def test_single_object():
    stream = BytesIO()
    savemat(stream, {'A':np.array(1, dtype=object)})


def test_skip_variable():
    # Test skipping over the first of two variables in a MAT file
    # using mat_reader_factory and put_variables to read them in.
    #
    # This is a regression test of a problem that's caused by
    # using the compressed file reader seek instead of the raw file
    # I/O seek when skipping over a compressed chunk.
    #
    # The problem arises when the chunk is large: this file has
    # a 256x256 array of random (uncompressible) doubles.
    #
    filename = pjoin(test_data_path,'test_skip_variable.mat')
    #
    # Prove that it loads with loadmat
    #
    d = loadmat(filename, struct_as_record=True)
    assert_('first' in d)
    assert_('second' in d)
    #
    # Make the factory
    #
    factory, file_opened = mat_reader_factory(filename, struct_as_record=True)
    #
    # This is where the factory breaks with an error in MatMatrixGetter.to_next
    #
    d = factory.get_variables('second')
    assert_('second' in d)
    factory.mat_stream.close()


def test_empty_struct():
    # ticket 885
    filename = pjoin(test_data_path,'test_empty_struct.mat')
    # before ticket fix, this would crash with ValueError, empty data
    # type
    d = loadmat(filename, struct_as_record=True)
    a = d['a']
    assert_equal(a.shape, (1,1))
    assert_equal(a.dtype, np.dtype(object))
    assert_(a[0,0] is None)
    stream = BytesIO()
    arr = np.array((), dtype='U')
    # before ticket fix, this used to give data type not understood
    savemat(stream, {'arr':arr})
    d = loadmat(stream)
    a2 = d['arr']
    assert_array_equal(a2, arr)


def test_save_empty_dict():
    # saving empty dict also gives empty struct
    stream = BytesIO()
    savemat(stream, {'arr': {}})
    d = loadmat(stream)
    a = d['arr']
    assert_equal(a.shape, (1,1))
    assert_equal(a.dtype, np.dtype(object))
    assert_(a[0,0] is None)


def assert_any_equal(output, alternatives):
    """ Assert `output` is equal to at least one element in `alternatives`
    """
    one_equal = False
    for expected in alternatives:
        if np.all(output == expected):
            one_equal = True
            break
    assert_(one_equal)


def test_to_writeable():
    # Test to_writeable function
    res = to_writeable(np.array([1]))  # pass through ndarrays
    assert_equal(res.shape, (1,))
    assert_array_equal(res, 1)
    # Dict fields can be written in any order
    expected1 = np.array([(1, 2)], dtype=[('a', '|O8'), ('b', '|O8')])
    expected2 = np.array([(2, 1)], dtype=[('b', '|O8'), ('a', '|O8')])
    alternatives = (expected1, expected2)
    assert_any_equal(to_writeable({'a':1,'b':2}), alternatives)
    # Fields with underscores discarded with a warning message.
    with pytest.warns(MatWriteWarning, match='Starting field name with'):
        assert_any_equal(to_writeable({'a':1, 'b':2, '_c':3}), alternatives)
    # Not-string fields discarded
    assert_any_equal(to_writeable({'a':1,'b':2, 100:3}), alternatives)
    # String fields that are valid Python identifiers discarded
    with pytest.warns(MatWriteWarning, match='Starting field name with'):
        assert_any_equal(to_writeable({'a':1, 'b':2, '99':3}), alternatives)
    # Object with field names is equivalent

    class klass:
        pass

    c = klass
    c.a = 1
    c.b = 2
    assert_any_equal(to_writeable(c), alternatives)
    # empty list and tuple go to empty array
    res = to_writeable([])
    assert_equal(res.shape, (0,))
    assert_equal(res.dtype.type, np.float64)
    res = to_writeable(())
    assert_equal(res.shape, (0,))
    assert_equal(res.dtype.type, np.float64)
    # None -> None
    assert_(to_writeable(None) is None)
    # String to strings
    assert_equal(to_writeable('a string').dtype.type, np.str_)
    # Scalars to numpy to NumPy scalars
    res = to_writeable(1)
    assert_equal(res.shape, ())
    assert_equal(res.dtype.type, np.array(1).dtype.type)
    assert_array_equal(res, 1)
    # Empty dict returns EmptyStructMarker
    assert_(to_writeable({}) is EmptyStructMarker)
    # Object does not have (even empty) __dict__
    assert_(to_writeable(object()) is None)
    # Custom object does have empty __dict__, returns EmptyStructMarker

    class C:
        pass

    assert_(to_writeable(c()) is EmptyStructMarker)
    # dict keys with legal characters are convertible
    res = to_writeable({'a': 1})['a']
    assert_equal(res.shape, (1,))
    assert_equal(res.dtype.type, np.object_)
    # Only fields with illegal characters, falls back to EmptyStruct
    with pytest.warns(MatWriteWarning, match='Starting field name with'):
        assert_(to_writeable({'1':1}) is EmptyStructMarker)

    with pytest.warns(MatWriteWarning, match='Starting field name with'):
        assert_(to_writeable({'_a':1}) is EmptyStructMarker)
    # Unless there are valid fields, in which case structured array
    with pytest.warns(MatWriteWarning, match='Starting field name with'):
        assert_equal(to_writeable({'1':1, 'f': 2}),
                 np.array([(2,)], dtype=[('f', '|O8')]))


def test_recarray():
    # check roundtrip of structured array
    dt = [('f1', 'f8'),
          ('f2', 'S10')]
    arr = np.zeros((2,), dtype=dt)
    arr[0]['f1'] = 0.5
    arr[0]['f2'] = 'python'
    arr[1]['f1'] = 99
    arr[1]['f2'] = 'not perl'
    stream = BytesIO()
    savemat(stream, {'arr': arr})
    d = loadmat(stream, struct_as_record=False)
    a20 = d['arr'][0,0]
    assert_equal(a20.f1, 0.5)
    assert_equal(a20.f2, 'python')
    d = loadmat(stream, struct_as_record=True)
    a20 = d['arr'][0,0]
    assert_equal(a20['f1'], 0.5)
    assert_equal(a20['f2'], 'python')
    # structs always come back as object types
    assert_equal(a20.dtype, np.dtype([('f1', 'O'),
                                      ('f2', 'O')]))
    a21 = d['arr'].flat[1]
    assert_equal(a21['f1'], 99)
    assert_equal(a21['f2'], 'not perl')


def test_save_object():
    class C:
        pass
    c = C()
    c.field1 = 1
    c.field2 = 'a string'
    stream = BytesIO()
    savemat(stream, {'c': c})
    d = loadmat(stream, struct_as_record=False)
    c2 = d['c'][0,0]
    assert_equal(c2.field1, 1)
    assert_equal(c2.field2, 'a string')
    d = loadmat(stream, struct_as_record=True)
    c2 = d['c'][0,0]
    assert_equal(c2['field1'], 1)
    assert_equal(c2['field2'], 'a string')


def test_read_opts():
    # tests if read is seeing option sets, at initialization and after
    # initialization
    arr = np.arange(6).reshape(1,6)
    stream = BytesIO()
    savemat(stream, {'a': arr})
    rdr = MatFile5Reader(stream)
    back_dict = rdr.get_variables()
    rarr = back_dict['a']
    assert_array_equal(rarr, arr)
    rdr = MatFile5Reader(stream, squeeze_me=True)
    assert_array_equal(rdr.get_variables()['a'], arr.reshape((6,)))
    rdr.squeeze_me = False
    assert_array_equal(rarr, arr)
    rdr = MatFile5Reader(stream, byte_order=boc.native_code)
    assert_array_equal(rdr.get_variables()['a'], arr)
    # inverted byte code leads to error on read because of swapped
    # header etc.
    rdr = MatFile5Reader(stream, byte_order=boc.swapped_code)
    assert_raises(Exception, rdr.get_variables)
    rdr.byte_order = boc.native_code
    assert_array_equal(rdr.get_variables()['a'], arr)
    arr = np.array(['a string'])
    stream.truncate(0)
    stream.seek(0)
    savemat(stream, {'a': arr})
    rdr = MatFile5Reader(stream)
    assert_array_equal(rdr.get_variables()['a'], arr)
    rdr = MatFile5Reader(stream, chars_as_strings=False)
    carr = np.atleast_2d(np.array(list(arr.item()), dtype='U1'))
    assert_array_equal(rdr.get_variables()['a'], carr)
    rdr.chars_as_strings = True
    assert_array_equal(rdr.get_variables()['a'], arr)


def test_empty_string():
    # make sure reading empty string does not raise error
    estring_fname = pjoin(test_data_path, 'single_empty_string.mat')
    fp = open(estring_fname, 'rb')
    rdr = MatFile5Reader(fp)
    d = rdr.get_variables()
    fp.close()
    assert_array_equal(d['a'], np.array([], dtype='U1'))
    # Empty string round trip. Matlab cannot distinguish
    # between a string array that is empty, and a string array
    # containing a single empty string, because it stores strings as
    # arrays of char. There is no way of having an array of char that
    # is not empty, but contains an empty string.
    stream = BytesIO()
    savemat(stream, {'a': np.array([''])})
    rdr = MatFile5Reader(stream)
    d = rdr.get_variables()
    assert_array_equal(d['a'], np.array([], dtype='U1'))
    stream.truncate(0)
    stream.seek(0)
    savemat(stream, {'a': np.array([], dtype='U1')})
    rdr = MatFile5Reader(stream)
    d = rdr.get_variables()
    assert_array_equal(d['a'], np.array([], dtype='U1'))
    stream.close()


def test_corrupted_data():
    import zlib
    for exc, fname in [(ValueError, 'corrupted_zlib_data.mat'),
                       (zlib.error, 'corrupted_zlib_checksum.mat')]:
        with open(pjoin(test_data_path, fname), 'rb') as fp:
            rdr = MatFile5Reader(fp)
            assert_raises(exc, rdr.get_variables)


def test_corrupted_data_check_can_be_disabled():
    with open(pjoin(test_data_path, 'corrupted_zlib_data.mat'), 'rb') as fp:
        rdr = MatFile5Reader(fp, verify_compressed_data_integrity=False)
        rdr.get_variables()


def test_read_both_endian():
    # make sure big- and little- endian data is read correctly
    for fname in ('big_endian.mat', 'little_endian.mat'):
        fp = open(pjoin(test_data_path, fname), 'rb')
        rdr = MatFile5Reader(fp)
        d = rdr.get_variables()
        fp.close()
        assert_array_equal(d['strings'],
                           np.array([['hello'],
                                     ['world']], dtype=object))
        assert_array_equal(d['floats'],
                           np.array([[2., 3.],
                                     [3., 4.]], dtype=np.float32))


def test_write_opposite_endian():
    # We don't support writing opposite endian .mat files, but we need to behave
    # correctly if the user supplies an other-endian NumPy array to write out.
    float_arr = np.array([[2., 3.],
                          [3., 4.]])
    int_arr = np.arange(6).reshape((2, 3))
    uni_arr = np.array(['hello', 'world'], dtype='U')
    stream = BytesIO()
    savemat(stream, {
        'floats': float_arr.byteswap().view(float_arr.dtype.newbyteorder()),
        'ints': int_arr.byteswap().view(int_arr.dtype.newbyteorder()),
        'uni_arr': uni_arr.byteswap().view(uni_arr.dtype.newbyteorder()),
    })
    rdr = MatFile5Reader(stream)
    d = rdr.get_variables()
    assert_array_equal(d['floats'], float_arr)
    assert_array_equal(d['ints'], int_arr)
    assert_array_equal(d['uni_arr'], uni_arr)
    stream.close()


def test_logical_array():
    # The roundtrip test doesn't verify that we load the data up with the
    # correct (bool) dtype
    with open(pjoin(test_data_path, 'testbool_8_WIN64.mat'), 'rb') as fobj:
        rdr = MatFile5Reader(fobj, mat_dtype=True)
        d = rdr.get_variables()
    x = np.array([[True], [False]], dtype=np.bool_)
    assert_array_equal(d['testbools'], x)
    assert_equal(d['testbools'].dtype, x.dtype)


def test_logical_out_type():
    # Confirm that bool type written as uint8, uint8 class
    # See gh-4022
    stream = BytesIO()
    barr = np.array([False, True, False])
    savemat(stream, {'barray': barr})
    stream.seek(0)
    reader = MatFile5Reader(stream)
    reader.initialize_read()
    reader.read_file_header()
    hdr, _ = reader.read_var_header()
    assert_equal(hdr.mclass, mio5p.mxUINT8_CLASS)
    assert_equal(hdr.is_logical, True)
    var = reader.read_var_array(hdr, False)
    assert_equal(var.dtype.type, np.uint8)


def test_roundtrip_zero_dimensions():
    stream = BytesIO()
    savemat(stream, {'d':np.empty((10, 0))})
    d = loadmat(stream)
    assert d['d'].shape == (10, 0)


def test_mat4_3d():
    # test behavior when writing 3-D arrays to matlab 4 files
    stream = BytesIO()
    arr = np.arange(24).reshape((2,3,4))
    assert_raises(ValueError, savemat, stream, {'a': arr}, True, '4')


def test_func_read():
    func_eg = pjoin(test_data_path, 'testfunc_7.4_GLNX86.mat')
    fp = open(func_eg, 'rb')
    rdr = MatFile5Reader(fp)
    d = rdr.get_variables()
    fp.close()
    assert isinstance(d['testfunc'], MatlabFunction)
    stream = BytesIO()
    wtr = MatFile5Writer(stream)
    # This test mat file has `__header__` field.
    with pytest.warns(MatWriteWarning, match='Starting field name with'):
        assert_raises(MatWriteError, wtr.put_variables, d)


def test_mat_dtype():
    double_eg = pjoin(test_data_path, 'testmatrix_6.1_SOL2.mat')
    fp = open(double_eg, 'rb')
    rdr = MatFile5Reader(fp, mat_dtype=False)
    d = rdr.get_variables()
    fp.close()
    assert_equal(d['testmatrix'].dtype.kind, 'u')

    fp = open(double_eg, 'rb')
    rdr = MatFile5Reader(fp, mat_dtype=True)
    d = rdr.get_variables()
    fp.close()
    assert_equal(d['testmatrix'].dtype.kind, 'f')


def test_sparse_in_struct():
    # reproduces bug found by DC where Cython code was insisting on
    # ndarray return type, but getting sparse matrix
    st = {'sparsefield': eye_array(4)}
    stream = BytesIO()
    savemat(stream, {'a':st})
    d = loadmat(stream, struct_as_record=True)
    assert_array_equal(d['a'][0, 0]['sparsefield'].toarray(), np.eye(4))


def test_mat_struct_squeeze():
    stream = BytesIO()
    in_d = {'st':{'one':1, 'two':2}}
    savemat(stream, in_d)
    # no error without squeeze
    loadmat(stream, struct_as_record=False)
    # previous error was with squeeze, with mat_struct
    loadmat(stream, struct_as_record=False, squeeze_me=True)


def test_scalar_squeeze():
    stream = BytesIO()
    in_d = {'scalar': [[0.1]], 'string': 'my name', 'st':{'one':1, 'two':2}}
    savemat(stream, in_d)
    out_d = loadmat(stream, squeeze_me=True)
    assert_(isinstance(out_d['scalar'], float))
    assert_(isinstance(out_d['string'], str))
    assert_(isinstance(out_d['st'], np.ndarray))


def test_str_round():
    # from report by Angus McMorland on mailing list 3 May 2010
    stream = BytesIO()
    in_arr = np.array(['Hello', 'Foob'])
    out_arr = np.array(['Hello', 'Foob '])
    savemat(stream, dict(a=in_arr))
    res = loadmat(stream)
    # resulted in ['HloolFoa', 'elWrdobr']
    assert_array_equal(res['a'], out_arr)
    stream.truncate(0)
    stream.seek(0)
    # Make Fortran ordered version of string
    in_str = in_arr.tobytes(order='F')
    in_from_str = np.ndarray(shape=a.shape,
                             dtype=in_arr.dtype,
                             order='F',
                             buffer=in_str)
    savemat(stream, dict(a=in_from_str))
    assert_array_equal(res['a'], out_arr)
    # unicode save did lead to buffer too small error
    stream.truncate(0)
    stream.seek(0)
    in_arr_u = in_arr.astype('U')
    out_arr_u = out_arr.astype('U')
    savemat(stream, {'a': in_arr_u})
    res = loadmat(stream)
    assert_array_equal(res['a'], out_arr_u)


def test_fieldnames():
    # Check that field names are as expected
    stream = BytesIO()
    savemat(stream, {'a': {'a':1, 'b':2}})
    res = loadmat(stream)
    field_names = res['a'].dtype.names
    assert_equal(set(field_names), {'a', 'b'})


def test_loadmat_varnames():
    # Test that we can get just one variable from a mat file using loadmat
    mat5_sys_names = ['__globals__',
                      '__header__',
                      '__version__']
    for eg_file, sys_v_names in (
        (pjoin(test_data_path, 'testmulti_4.2c_SOL2.mat'), []), (pjoin(
            test_data_path, 'testmulti_7.4_GLNX86.mat'), mat5_sys_names)):
        vars = loadmat(eg_file)
        assert_equal(set(vars.keys()), set(['a', 'theta'] + sys_v_names))
        vars = loadmat(eg_file, variable_names='a')
        assert_equal(set(vars.keys()), set(['a'] + sys_v_names))
        vars = loadmat(eg_file, variable_names=['a'])
        assert_equal(set(vars.keys()), set(['a'] + sys_v_names))
        vars = loadmat(eg_file, variable_names=['theta'])
        assert_equal(set(vars.keys()), set(['theta'] + sys_v_names))
        vars = loadmat(eg_file, variable_names=('theta',))
        assert_equal(set(vars.keys()), set(['theta'] + sys_v_names))
        vars = loadmat(eg_file, variable_names=[])
        assert_equal(set(vars.keys()), set(sys_v_names))
        vnames = ['theta']
        vars = loadmat(eg_file, variable_names=vnames)
        assert_equal(vnames, ['theta'])


def test_round_types():
    # Check that saving, loading preserves dtype in most cases
    arr = np.arange(10)
    stream = BytesIO()
    for dts in ('f8','f4','i8','i4','i2','i1',
                'u8','u4','u2','u1','c16','c8'):
        stream.truncate(0)
        stream.seek(0)  # needed for BytesIO in Python 3
        savemat(stream, {'arr': arr.astype(dts)})
        vars = loadmat(stream)
        assert_equal(np.dtype(dts), vars['arr'].dtype)


def test_varmats_from_mat():
    # Make a mat file with several variables, write it, read it back
    names_vars = (('arr', mlarr(np.arange(10))),
                  ('mystr', mlarr('a string')),
                  ('mynum', mlarr(10)))

    # Dict like thing to give variables in defined order
    class C:
        def items(self):
            return names_vars
    stream = BytesIO()
    savemat(stream, C())
    varmats = varmats_from_mat(stream)
    assert_equal(len(varmats), 3)
    for i in range(3):
        name, var_stream = varmats[i]
        exp_name, exp_res = names_vars[i]
        assert_equal(name, exp_name)
        res = loadmat(var_stream)
        assert_array_equal(res[name], exp_res)


def test_one_by_zero():
    # Test 1x0 chars get read correctly
    func_eg = pjoin(test_data_path, 'one_by_zero_char.mat')
    fp = open(func_eg, 'rb')
    rdr = MatFile5Reader(fp)
    d = rdr.get_variables()
    fp.close()
    assert_equal(d['var'].shape, (0,))


def test_load_mat4_le():
    # We were getting byte order wrong when reading little-endian floa64 dense
    # matrices on big-endian platforms
    mat4_fname = pjoin(test_data_path, 'test_mat4_le_floats.mat')
    vars = loadmat(mat4_fname)
    assert_array_equal(vars['a'], [[0.1, 1.2]])


def test_unicode_mat4():
    # Mat4 should save unicode as latin1
    bio = BytesIO()
    var = {'second_cat': 'Schrödinger'}
    savemat(bio, var, format='4')
    var_back = loadmat(bio)
    assert_equal(var_back['second_cat'], var['second_cat'])


def test_logical_sparse():
    # Test we can read logical sparse stored in mat file as bytes.
    # See https://github.com/scipy/scipy/issues/3539.
    # In some files saved by MATLAB, the sparse data elements (Real Part
    # Subelement in MATLAB speak) are stored with apparent type double
    # (miDOUBLE) but are in fact single bytes.
    filename = pjoin(test_data_path,'logical_sparse.mat')
    # Before fix, this would crash with:
    # ValueError: indices and data should have the same size
    d = loadmat(filename, struct_as_record=True, spmatrix=False)
    log_sp = d['sp_log_5_4']
    assert_(issparse(log_sp) and log_sp.format == "csc")
    assert_equal(log_sp.dtype.type, np.bool_)
    assert_array_equal(log_sp.toarray(),
                       [[True, True, True, False],
                        [False, False, True, False],
                        [False, False, True, False],
                        [False, False, False, False],
                        [False, False, False, False]])


def test_empty_sparse():
    # Can we read empty sparse matrices?
    sio = BytesIO()
    import scipy.sparse
    empty_sparse = scipy.sparse.csr_array([[0,0],[0,0]])
    savemat(sio, dict(x=empty_sparse))
    sio.seek(0)

    res = loadmat(sio, spmatrix=False)
    assert not scipy.sparse.isspmatrix(res['x'])
    res = loadmat(sio, spmatrix=True)
    assert scipy.sparse.isspmatrix(res['x'])
    res = loadmat(sio)  # chk default
    assert scipy.sparse.isspmatrix(res['x'])

    assert_array_equal(res['x'].shape, empty_sparse.shape)
    assert_array_equal(res['x'].toarray(), 0)
    # Do empty sparse matrices get written with max nnz 1?
    # See https://github.com/scipy/scipy/issues/4208
    sio.seek(0)
    reader = MatFile5Reader(sio)
    reader.initialize_read()
    reader.read_file_header()
    hdr, _ = reader.read_var_header()
    assert_equal(hdr.nzmax, 1)


def test_empty_mat_error():
    # Test we get a specific warning for an empty mat file
    sio = BytesIO()
    assert_raises(MatReadError, loadmat, sio)


def test_miuint32_compromise():
    # Reader should accept miUINT32 for miINT32, but check signs
    # mat file with miUINT32 for miINT32, but OK values
    filename = pjoin(test_data_path, 'miuint32_for_miint32.mat')
    res = loadmat(filename)
    assert_equal(res['an_array'], np.arange(10)[None, :])
    # mat file with miUINT32 for miINT32, with negative value
    filename = pjoin(test_data_path, 'bad_miuint32.mat')
    with assert_raises(ValueError):
        loadmat(filename)


def test_miutf8_for_miint8_compromise():
    # Check reader accepts ascii as miUTF8 for array names
    filename = pjoin(test_data_path, 'miutf8_array_name.mat')
    res = loadmat(filename)
    assert_equal(res['array_name'], [[1]])
    # mat file with non-ascii utf8 name raises error
    filename = pjoin(test_data_path, 'bad_miutf8_array_name.mat')
    with assert_raises(ValueError):
        loadmat(filename)


def test_bad_utf8():
    # Check that reader reads bad UTF with 'replace' option
    filename = pjoin(test_data_path,'broken_utf8.mat')
    res = loadmat(filename)
    assert_equal(res['bad_string'],
                 b'\x80 am broken'.decode('utf8', 'replace'))


def test_save_unicode_field(tmpdir):
    filename = os.path.join(str(tmpdir), 'test.mat')
    test_dict = {'a':{'b':1,'c':'test_str'}}
    savemat(filename, test_dict)


def test_save_custom_array_type(tmpdir):
    class CustomArray:
        def __array__(self, dtype=None, copy=None):
            return np.arange(6.0).reshape(2, 3)
    a = CustomArray()
    filename = os.path.join(str(tmpdir), 'test.mat')
    savemat(filename, {'a': a})
    out = loadmat(filename)
    assert_array_equal(out['a'], np.array(a))


def test_filenotfound():
    # Check the correct error is thrown
    assert_raises(OSError, loadmat, "NotExistentFile00.mat")
    assert_raises(OSError, loadmat, "NotExistentFile00")


def test_simplify_cells():
    # Test output when simplify_cells=True
    filename = pjoin(test_data_path, 'testsimplecell.mat')
    res1 = loadmat(filename, simplify_cells=True)
    res2 = loadmat(filename, simplify_cells=False)
    assert_(isinstance(res1["s"], dict))
    assert_(isinstance(res2["s"], np.ndarray))
    assert_array_equal(res1["s"]["mycell"], np.array(["a", "b", "c"]))


@pytest.mark.parametrize('version, filt, regex', [
    (0, '_4*_*', None),
    (1, '_5*_*', None),
    (1, '_6*_*', None),
    (1, '_7*_*', '^((?!hdf5).)*$'),  # not containing hdf5
    (2, '_7*_*', '.*hdf5.*'),
    (1, '8*_*', None),
])
def test_matfile_version(version, filt, regex):
    use_filt = pjoin(test_data_path, f'test*{filt}.mat')
    files = glob(use_filt)
    if regex is not None:
        files = [file for file in files if re.match(regex, file) is not None]
    assert len(files) > 0, \
        f"No files for version {version} using filter {filt}"
    for file in files:
        got_version = matfile_version(file)
        assert got_version[0] == version


def test_opaque():
    """Test that we can read a MatlabOpaque object."""
    data = loadmat(pjoin(test_data_path, 'parabola.mat'))
    assert isinstance(data['parabola'], MatlabFunction)
    assert isinstance(data['parabola'].item()[3].item()[3], MatlabOpaque)


def test_opaque_simplify():
    """Test that we can read a MatlabOpaque object when simplify_cells=True."""
    data = loadmat(pjoin(test_data_path, 'parabola.mat'), simplify_cells=True)
    assert isinstance(data['parabola'], MatlabFunction)


def test_deprecation():
    """Test that access to previous attributes still works."""
    # This should be accessible immediately from scipy.io import
    with assert_warns(DeprecationWarning):
        scipy.io.matlab.mio5_params.MatlabOpaque

    # These should be importable but warn as well
    with assert_warns(DeprecationWarning):
        from scipy.io.matlab.miobase import MatReadError  # noqa: F401


def test_gh_17992(tmp_path):
    rng = np.random.default_rng(12345)
    outfile = tmp_path / "lists.mat"
    array_one = rng.random((5,3))
    array_two = rng.random((6,3))
    list_of_arrays = [array_one, array_two]
    savemat(outfile,
            {'data': list_of_arrays},
            long_field_names=True,
            do_compression=True)
    # round trip check
    new_dict = {}
    loadmat(outfile,
            new_dict)
    assert_allclose(new_dict["data"][0][0], array_one)
    assert_allclose(new_dict["data"][0][1], array_two)


def test_gh_19659(tmp_path):
    d = {
        "char_array": np.array([list("char"), list("char")], dtype="U1"),
        "string_array": np.array(["string", "string"]),
        }
    outfile = tmp_path / "tmp.mat"
    # should not error:
    savemat(outfile, d, format="4")


def test_large_m4():
    # Test we can read a Matlab 4 file with array > 2GB.
    # (In fact, test we get the correct error from reading a truncated
    # version).
    # See https://github.com/scipy/scipy/issues/21256
    # Data file is first 1024 bytes of:
    # >>> a = np.zeros((134217728, 3))
    # >>> siom.savemat('big_m4.mat', {'a': a}, format='4')
    truncated_mat = pjoin(test_data_path, 'debigged_m4.mat')
    match = ("Not enough bytes to read matrix 'a';"
             if np.intp == np.int64 else
             "Variable 'a' has byte length longer than largest possible")
    with pytest.raises(ValueError, match=match):
        loadmat(truncated_mat)


def test_gh_19223():
    from scipy.io.matlab import varmats_from_mat  # noqa: F401


def test_invalid_field_name_warning():
    names_vars = (
        ('_1', mlarr(np.arange(10))),
        ('mystr', mlarr('a string')))
    check_mat_write_warning(names_vars)

    names_vars = (('mymap', {"a": 1, "_b": 2}),)
    check_mat_write_warning(names_vars)

    names_vars = (('mymap', {"a": 1, "1a": 2}),)
    check_mat_write_warning(names_vars)


def check_mat_write_warning(names_vars):
    class C:
        def items(self):
            return names_vars

    stream = BytesIO()
    with pytest.warns(MatWriteWarning, match='Starting field name with'):
        savemat(stream, C())


def test_corrupt_files():
    # Test we can detect truncated or corrupt (all zero) files.
    for n in (2, 4, 10, 19):
        with pytest.raises(MatReadError,
                           match="Mat file appears to be truncated"):
            loadmat(BytesIO(b'\x00' * n))
    with pytest.raises(MatReadError,
                       match="Mat file appears to be corrupt"):
        loadmat(BytesIO(b'\x00' * 20))
