Test suite fails with NameError

Running the test suite fails for 8 tests due to a NameError because the object under test isn't specified correctly:

$ python -m unittest discover pydv.tests -k GPSTime
/home/duncan/opt/mambaforge/envs/py310/lib/python3.10/site-packages/matplotlib/__init__.py:152: DeprecationWarning: distutils Version classes are deprecated. Use packaging.version instead.
  if LooseVersion(module.__version__) < minver:
/home/duncan/opt/mambaforge/envs/py310/lib/python3.10/site-packages/setuptools/_distutils/version.py:351: DeprecationWarning: distutils Version classes are deprecated. Use packaging.version instead.
  other = LooseVersion(other)
EEEEEEEE
======================================================================
ERROR: test_casting (pydv.tests.TestGPSTime)
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Traceback (most recent call last):
  File "/home/duncan/opt/mambaforge/envs/py310/lib/python3.10/site-packages/pydv/tests.py", line 117, in setUp
    self.now = GPSTime()
NameError: name 'GPSTime' is not defined

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ERROR: test_equality_method (pydv.tests.TestGPSTime)
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Traceback (most recent call last):
  File "/home/duncan/opt/mambaforge/envs/py310/lib/python3.10/site-packages/pydv/tests.py", line 117, in setUp
    self.now = GPSTime()
NameError: name 'GPSTime' is not defined

======================================================================
ERROR: test_expected_BadGPSTime_exception (pydv.tests.TestGPSTime)
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Traceback (most recent call last):
  File "/home/duncan/opt/mambaforge/envs/py310/lib/python3.10/site-packages/pydv/tests.py", line 117, in setUp
    self.now = GPSTime()
NameError: name 'GPSTime' is not defined

======================================================================
ERROR: test_expected_time_difference (pydv.tests.TestGPSTime)
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Traceback (most recent call last):
  File "/home/duncan/opt/mambaforge/envs/py310/lib/python3.10/site-packages/pydv/tests.py", line 117, in setUp
    self.now = GPSTime()
NameError: name 'GPSTime' is not defined

======================================================================
ERROR: test_expected_time_sum (pydv.tests.TestGPSTime)
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Traceback (most recent call last):
  File "/home/duncan/opt/mambaforge/envs/py310/lib/python3.10/site-packages/pydv/tests.py", line 117, in setUp
    self.now = GPSTime()
NameError: name 'GPSTime' is not defined

======================================================================
ERROR: test_greater (pydv.tests.TestGPSTime)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/duncan/opt/mambaforge/envs/py310/lib/python3.10/site-packages/pydv/tests.py", line 117, in setUp
    self.now = GPSTime()
NameError: name 'GPSTime' is not defined

======================================================================
ERROR: test_less (pydv.tests.TestGPSTime)
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Traceback (most recent call last):
  File "/home/duncan/opt/mambaforge/envs/py310/lib/python3.10/site-packages/pydv/tests.py", line 117, in setUp
    self.now = GPSTime()
NameError: name 'GPSTime' is not defined

======================================================================
ERROR: test_type_after_sum (pydv.tests.TestGPSTime)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/duncan/opt/mambaforge/envs/py310/lib/python3.10/site-packages/pydv/tests.py", line 117, in setUp
    self.now = GPSTime()
NameError: name 'GPSTime' is not defined

----------------------------------------------------------------------
Ran 8 tests in 0.001s

FAILED (errors=8)