Add unit tests for exception handling

[Beeram12]

fixes #147

1. This adds unit tests for exception.py .

[gemini-code-assist]

Code Review

This pull request unignores the tests/ directory and introduces a new test suite for the project's custom exception hierarchy. The feedback focuses on improving test accuracy by fixing a typo and directly verifying attributes, adhering to PEP 8 standards for None comparisons, and ensuring complete coverage of the exception hierarchy by adding a test for VectorStoreValidationError.

[gemini-code-assist]

The test name test_mssg_attribute_is_accessible contains a typo (mssg) and the implementation redundantly checks the string representation instead of the actual message attribute. It should be updated to verify the attribute directly.

Suggested change

	def test_mssg_attribute_is_accessible(self):
	err = XMemError("hello")
	assert str(err) == "hello"
	def test_message_attribute_is_accessible(self):
	err = XMemError("hello")
	assert err.message == "hello"

[gemini-code-assist]

According to PEP 8, comparisons to singletons like None should always be done with is or is not, never the equality operators.

Suggested change

	assert err.operation == None
	assert err.operation is None

References

1. Comparisons to singletons like None should always be done with 'is' or 'is not', never the equality operators. ^(link)

[gemini-code-assist]

The VectorStoreValidationError class is imported but not included in the hierarchy tests. It's important to verify that it correctly inherits from VectorStoreError to ensure the exception hierarchy is functioning as expected.

Suggested change

	def test_validation_error_is_not_a_vector_store_error(self):
	err = ValidationError("bad input")
	assert not isinstance(err, VectorStoreError)
	def test_vector_store_validation_error_is_caught_as_vector_store_error(self):
	with pytest.raises(VectorStoreError):
	raise VectorStoreValidationError("invalid metadata")
	def test_validation_error_is_not_a_vector_store_error(self):
	err = ValidationError("bad input")
	assert not isinstance(err, VectorStoreError)