Fix indentation errors in tests

[victorprincipe]

In lots of the tests, an exception was caught as shown below, with an assertEqual to ensure that the error message matches what the exception that is caught:

with self.assertRaises(ValueError) as cm:
            _ = PCovFPS(n_to_select=1, mixing=1.0)
            self.assertEqual(
                str(cm.exception),
                "Mixing = 1.0 corresponds to traditional FPS." "Please use the FPS class.",
            )

However, when the exception is caught (at _ = PCovFPS(n_to_select=1, mixing=1.0) in the example above), the rest of the code in the with method does not execute, and so the assertEqual tests were not run.

I have fixed these indentation errors in the following manner, for the example above:

with self.assertRaises(ValueError) as cm:
            _ = PCovFPS(n_to_select=1, mixing=1.0)
self.assertEqual(
    str(cm.exception),
    "Mixing = 1.0 corresponds to traditional FPS." "Please use the FPS class.",
)

Once the code executed properly, I additionally fixed some tests that were not functioning properly or raising warnings. Examples of errors that led to failed tests/warnings include:

• Using self.assertTrue() rather than self.assertEqual()
• Typos in the string passed to self.assertEqual()
• Using self.assertEquals() rather than self.assertEqual()(Deprecation warning)
• Forgetting to fit a GreedySelector in the test (when the test was not meant to check this error, obviously)

I also made some minor changes/typo fixes to error messages in the VoronoiFPS and SparseKernelCenterer classes.