Add some more tests

[caldempsey]

Adds a few negative tests. These two are suspect:

def test_to_from_base62_invalid_base62_string():
    # Arrange
    ksuid = Ksuid()
    invalid_base62 = "invalid_base62_string!"

    # Act & Assert
    with pytest.raises(ValueError):
        ksuid.from_base62(invalid_base62)

def test_to_from_base62_empty_string():
    # Arrange
    ksuid = Ksuid()
    empty_base62 = ""

    # Act & Assert
    with pytest.raises(IndexError): # this looks wrong
        ksuid.from_base62(empty_base62)

[svix-jplatte]

Trying to get CI to run..

[svix-jplatte]

Wait, I'm a bit confused. Did these pass originally? The IndexError one at least looks like it's meant to be mergable and document the status quo so any changes to that behavior would have a test that would confirm the intended change.

[svix-jbrown]

Wait, I'm a bit confused. Did these pass originally? The IndexError one at least looks like it's meant to be mergable and document the status quo so any changes to that behavior would have a test that would confirm the intended change.

We made some big changes to this library since this PR was submitted 2 years ago...

[caldempsey]

Don't believe they passed originally no.