What is an assertion?

What is an "assertion framework"?

• I was reading about the js-test-driver unit-testing framework, when I found out that the guys behind the framework intend it to be http://code.google.com/p/js-test-driver/wiki/XUnitCompatibility. What is an assertion framework? Is it a kind of unit-testing framework? If it is the case what is specific to such frameworks?

• Answer:

  An example of an Assertion Framework would be http://code.google.com/p/hamcrest/ which was integrated into JUnit 4. Hamcrest does not run tests, it merely provides an expressive way to write assertions. Old JUnit style equality assertion: assertEquals(constant, underTest); // or for doubles assertEquals(3.5, underTest, .001); // within 1/1000th Hamcrest style equality assertions: assertThat(underTest, Is.EqualTo(constant)); // or for doubles assertThat(underTest, Is.EqualTo(3.5).Within(.001)); Essentially, an assertion framework allows you to perform your assertions in an easily extensible manner. Because the assertion framework focuses on assertions alone, it can do the job much better than a tool that has to collect and run tests as well. NUnit has also adopted the Hamcrest approach to assertions. You would not use Hamcrest to run your tests, merely to write the assertions.