Used to assert that one value is less than another value.
The value to test.
The value it should be less than.
The file name that the assert failed in. Should be left as default.
The file line that the assert failed in. Should be left as default.
If the value is NOT less, will throw an AssertError with expected and actual values.
// Will throw an exception like "AssertError@example.d(6): <10> expected to be less than <5>." 10.shouldBeLess(5);