Adjust test imports to ensure all tests run once

Some classes had been missed from tests/__init__.py, meaning they were
skipped when running 'unittest tests'.

Others were being run multiple times because the classes themselves were
imported into other test modules and so they were being found by
'unittest discover' or 'pytest'. Importing them as modules instead
avoids this (thanks to https://stackoverflow.com/a/68976671)

tests/__init__.py

@@ -11,25 +11,28 @@
 
 from .test_bzip2mrcfile import Bzip2MrcFileTest
 from .test_command_line import CommandLineTest
+from .test_dtypes import DtypesTest
 from .test_future_mrcfile import FutureMrcFileTest
 from .test_gzipmrcfile import GzipMrcFileTest
-from .test_load_functions import LoadFunctionTest
-from .test_mrcobject import MrcObjectTest
-from .test_mrcinterpreter import MrcInterpreterTest
+from .test_load_functions import LoadFunctionTest, LoadFunctionTestWithPathlib
 from .test_mrcfile import MrcFileTest
+from .test_mrcinterpreter import MrcInterpreterTest
 from .test_mrcmemmap import MrcMemmapTest
+from .test_mrcobject import MrcObjectTest
 from .test_utils import UtilsTest
 from .test_validation import ValidationTest
 
 test_classes = [
     Bzip2MrcFileTest,
     CommandLineTest,
+    DtypesTest,
     FutureMrcFileTest,
     GzipMrcFileTest,
     LoadFunctionTest,
-    MrcObjectTest,
-    MrcInterpreterTest,
+    LoadFunctionTestWithPathlib,
     MrcFileTest,
+    MrcInterpreterTest,
+    MrcObjectTest,
     MrcMemmapTest,
     UtilsTest,
     ValidationTest

tests/test_bzip2mrcfile.py

@@ -12,11 +12,11 @@
 import os
 import unittest
 
-from .test_mrcfile import MrcFileTest
+from . import test_mrcfile
 from mrcfile.bzip2mrcfile import Bzip2MrcFile
 
 
-class Bzip2MrcFileTest(MrcFileTest):
+class Bzip2MrcFileTest(test_mrcfile.MrcFileTest):
 
     """Unit tests for bzip2 MRC file I/O.
     

tests/test_gzipmrcfile.py

@@ -12,11 +12,11 @@
 import os
 import unittest
 
-from .test_mrcfile import MrcFileTest
+from . import test_mrcfile
 from mrcfile.gzipmrcfile import GzipMrcFile
 
 
-class GzipMrcFileTest(MrcFileTest):
+class GzipMrcFileTest(test_mrcfile.MrcFileTest):
 
     """Unit tests for gzipped MRC file I/O.
     

tests/test_load_functions.py

@@ -103,10 +103,12 @@ def test_new_empty_file_with_open_function(self):
                                  .format(self.temp_mrc_name))
 
     def test_error_overwriting_file_with_open_function(self):
-        assert not os.path.exists(self.temp_mrc_name)
-        open(self.temp_mrc_name, 'w+').close()
-        assert os.path.exists(self.temp_mrc_name)
-        with self.assertRaisesRegex(ValueError, "call 'mrcfile\.new\(\)'"):
+        # Convert name to str to avoid TypeErrors in Python 2.7 with pathlib
+        temp_mrc_name_str = str(self.temp_mrc_name)
+        assert not os.path.exists(temp_mrc_name_str)
+        open(temp_mrc_name_str, 'w+').close()
+        assert os.path.exists(temp_mrc_name_str)
+        with self.assertRaisesRegex(ValueError, r"call 'mrcfile\.new\(\)'"):
             mrcfile.open(self.temp_mrc_name, mode='w+')
 
     def test_header_only_opening(self):

tests/test_mrcfile.py

@@ -22,8 +22,7 @@
 except ImportError:
     from numpy import ComplexWarning
 
-from . import helpers
-from .test_mrcobject import MrcObjectTest
+from . import helpers, test_mrcobject
 from mrcfile.mrcfile import MrcFile
 from mrcfile.mrcobject import (IMAGE_STACK_SPACEGROUP, VOLUME_SPACEGROUP,
                                VOLUME_STACK_SPACEGROUP)
@@ -58,7 +57,7 @@
 #     return tests
 
 
-class MrcFileTest(MrcObjectTest):
+class MrcFileTest(test_mrcobject.MrcObjectTest):
 
     """Unit tests for MRC file I/O.
 

tests/test_mrcinterpreter.py

@@ -15,12 +15,12 @@
 
 import numpy as np
 
-from .test_mrcobject import MrcObjectTest
+from . import test_mrcobject
 from mrcfile.constants import MAP_ID_OFFSET_BYTES
 from mrcfile.mrcinterpreter import MrcInterpreter
 
 
-class MrcInterpreterTest(MrcObjectTest):
+class MrcInterpreterTest(test_mrcobject.MrcObjectTest):
 
     """Unit tests for MrcInterpreter class.
     

tests/test_mrcmemmap.py

@@ -14,11 +14,11 @@
 
 import numpy as np
 
-from .test_mrcfile import MrcFileTest
+from . import test_mrcfile
 from mrcfile.mrcmemmap import MrcMemmap
 
 
-class MrcMemmapTest(MrcFileTest):
+class MrcMemmapTest(test_mrcfile.MrcFileTest):
 
     """Unit tests for MRC file I/O with memory-mapped files.