Java Extreme Programming Cookbook

Repeatedly Testing the Same Method

Problem

You want to test a method with a wide range of input data. You are not sure if you should write a different test for each combination of input data, or one huge test that checks every possible combination.

Solution

Write a suite( ) method that iterates through all of your input data, creating a unique instance of your test case for each unique input. The data is passed to the test cases through the constructor, which stores the data in instance fields so it is available to the test methods.

Discussion

You often want to test some piece of functionality with many different combinations of input data. Your first impulse might be to write a different test method for each possible combination of data; however, this is tedious and results in a lot of mundane coding. A second option is to write a single, big test method that checks every possible combination of input data. For example:

public void testSomething(  ) {
    Foo foo = new Foo(  );
    // test every possible combination of input data
    assertTrue(foo.doSomething(false, false, false);
    assertFalse(foo.doSomething(false, false, true);
    assertFalse(foo.doSomething(false, true, false);
    assertTrue(foo.doSomething(false, true, true);
    ...etc
}

This approach suffers from a fatal flaw. The problem is that the test stops executing as soon as the first assertion fails, so you won’t see all of the errors at once. Ideally, you want to easily set up a large number of test cases and run them all as independent tests. ...