Add fuzz test, property-based test, and table test for PV function

[paulzuradzki]

Description

This change request adds testing to the pv / present value function.

• Tests
  • Adds fuzz tests and property-based tests (PBT) using Hypothesis
  • Adds more example-based tests (with pytest.mark.parametrize)
  • The hope is that these tests can be extended to other functions as well.
• Add exception handling for InvalidOperation, TypeError, DivisionByZero, Overflow. ~I opted to mirror numpy and return -0.0. Arguably, we would want a runtime error and can ignore it in the fuzz tests.~

Context:

• We use fuzz tests for extreme value testing (e.g., empty values, very low, very high, or zero) using a randomized input generator.
• We use property-based tests to verify that certain conditions hold true across a range of inputs.
• I used type hints and Hypothesis Ghostwriter CLI feature to help write the strategy.
  • We can generate random np.ndarray of small dimensions, but this was a bit slow. I opted to test array-input directly (tests/test_financial.py::TestPV::test_pv_examples[rates_as_array).

Testing

If you want to select only the related tests, you can run them like so.

$ pytest tests/test_financial.py::TestPV -vv

tests/test_financial.py::TestPV::test_pv PASSED                                                                                                                                          [  9%]
tests/test_financial.py::TestPV::test_pv_decimal PASSED                                                                                                                                  [ 18%]
tests/test_financial.py::TestPV::test_pv_examples[default_fv_and_when] PASSED                                                                                                            [ 27%]
tests/test_financial.py::TestPV::test_pv_examples[specify_fv_and_when] PASSED                                                                                                            [ 36%]
tests/test_financial.py::TestPV::test_pv_examples[when_1] PASSED                                                                                                                         [ 45%]
tests/test_financial.py::TestPV::test_pv_examples[when_1_and_fv_1000] PASSED                                                                                                             [ 54%]
tests/test_financial.py::TestPV::test_pv_examples[fv>0] PASSED                                                                                                                           [ 63%]
tests/test_financial.py::TestPV::test_pv_examples[negative_rate] PASSED                                                                                                                  [ 72%]
tests/test_financial.py::TestPV::test_pv_examples[rates_as_array] PASSED                                                                                                                 [ 81%]
tests/test_financial.py::TestPV::test_pv_fuzz PASSED                                                                                                                                     [ 90%]
tests/test_financial.py::TestPV::test_pv_interest_rate_sensitivity PASSED                                                                                                                [100%]

====================================================================================== 11 passed in 0.82s ======================================================================================