AssertNotEqual

AssertNotEqual is a unit testing assertion used to verify that two values are not equal. It passes when the two values differ and fails when they are equal. The assertion is commonly provided as a method such as assertNotEqual(a, b, msg=None) on a test case object. The exact syntax and name can vary by framework, but the core idea is to enforce inequality between two expressions.

The operation typically relies on the language’s equality operator, using a != b or an equivalent comparison. If the values compare as equal, the assertion fails and the test reports an assertion error, often including an optional failure message for context.

Usage examples:

- In Python's unittest framework, you would write: self.assertNotEqual(a, b) or self.assertNotEqual(a, b, msg="custom failure message"). If a == b, the test fails.

- In other frameworks, the same concept is available under a similar name, sometimes with slight naming differences or additional overloads for custom messages or types.

Notes and considerations:

- The result depends on the objects’ equality semantics. If a and b are objects with custom __eq__ methods, their equality logic will determine whether the assertion passes or fails.

- AssertNotEqual is most appropriate when a test specifically requires two values to differ, such as ensuring a generated identifier is not reused or that a computed result differs from an expected baseline.

Related assertions include assertEqual, which tests for equality, and specialized variants like assertNotAlmostEqual for numeric values where approximate equality is a concern.