Suppose you need to repeatedly execute some test method in your unit test case, for example, you would like to test getPrice based on the first set of test data 5 times in test method test1() while for the second set of test data, only one time should be executed.
The below class RepeatDemoOne is a bad example, where this special LOOP operation is mixed with test method implementation.
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Ideally the test method should only contain the pure logic to operate on the method being tested. So we have a better solution RepeatDemoTwo:
It could easily be observed that now the test method test1 and test2 are rather clean: no more for LOOP and System.out.println exist any more.
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Instead, I put the LOOP logic and print out operation into class RepeatableRule which implements interface MethodRule. The concrete rule implementation is done by overriding method apply as below:
class RepeatableRule implements MethodRule{ int times = 1; String[] testMethods = null; RepeatableRule(int times, String[] testMethods){ this.times = times; this.testMethods = testMethods; } @Override public Statement apply(final Statement base, final FrameworkMethod method, Object target) { return new Statement() { @Override public void evaluate() throws Throwable { int loopTime = 1; if(Arrays.asList(testMethods).contains(method.getName())) { loopTime = times; } for(int i = 0; i < loopTime; i++ ) { base.evaluate(); System.out.println(method.getName() + " executed."); } } }; } } When I execute this test case, I can get exactly the same result as RepeatDemoOne:
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With the help of @Rule, we can achieve the same as @Test(expected=).
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For example, we can use an instance of class ExpectedException to manually declare within a test method itself that a test method expects a given type of exception class.
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Besides exception, we can also manually specify a sub string which is expected to appear in an error message, and add our custom error message in Junit report if a test method fails. See following code for example:
public class RuleWithException { @Rule public ExpectedException exp = ExpectedException.none(); @Test public void expectMessage() { exp.expectMessage("Hello World"); throw new RuntimeException("Hello World will throw exception."); } @Test public void expectCourse() { exp.expectCause(new BaseMatcher() { public boolean matches(Object item) { return item instanceof IllegalArgumentException; } @Override public void describeTo(org.hamcrest.Description description) { description.appendText("Expected exception with type IllegalArgumentException " + "raised in test method! "); } }); Throwable cause = new IllegalArgumentException("Cause Test."); throw new RuntimeException(cause); } } In this example, if we comment out line 46, the customed message defined in method describeTo will be printed out in JUnit console:
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