org.junit.rules
Class ExpectedException

 java.lang.Object org.junit.rules.ExpectedException 

All Implemented Interfaces:

TestRule

public class ExpectedException
extends Object
implements TestRule

The ExpectedException rule allows you to verify that your code throws a specific exception.

Usage

 public class SimpleExpectedExceptionTest { @Rule public ExpectedException thrown= ExpectedException.none(); @Test public void throwsNothing() { // no exception expected, none thrown: passes. } @Test public void throwsExceptionWithSpecificType() { thrown.expect(NullPointerException.class); throw new NullPointerException(); } }

You have to add the ExpectedException rule to your test. This doesn't affect your existing tests (see throwsNothing()). After specifiying the type of the expected exception your test is successful when such an exception is thrown and it fails if a different or no exception is thrown.

Instead of specifying the exception's type you can characterize the expected exception based on other criterias, too:

• The exception's message contains a specific text: expectMessage(String)
• The exception's message complies with a Hamcrest matcher: expectMessage(Matcher)
• The exception's cause complies with a Hamcrest matcher: expectCause(Matcher)
• The exception itself complies with a Hamcrest matcher: expect(Matcher)

You can combine any of the presented expect-methods. The test is successful if all specifications are met.

 @Test public void throwsException() { thrown.expect(NullPointerException.class); thrown.expectMessage("happened"); throw new NullPointerException("What happened?"); }

AssumptionViolatedExceptions

JUnit uses AssumptionViolatedExceptions for indicating that a test provides no useful information. (See Assume for more information.) You have to call assume methods before you set expectations of the ExpectedException rule. In this case the rule will not handle consume the exceptions and it can be handled by the framework. E.g. the following test is ignored by JUnit's default runner.

 @Test public void ignoredBecauseOfFailedAssumption() { assumeTrue(false); // throws AssumptionViolatedException thrown.expect(NullPointerException.class); }

AssertionErrors

JUnit uses AssertionErrors for indicating that a test is failing. You have to call assert methods before you set expectations of the ExpectedException rule, if they should be handled by the framework. E.g. the following test fails because of the assertTrue statement.

 @Test public void throwsUnhandled() { assertTrue(false); // throws AssertionError thrown.expect(NullPointerException.class); }

Missing Exceptions

By default missing exceptions are reported with an error message like "Expected test to throw an instance of foo". You can configure a different message by means of reportMissingExceptionWithMessage(String). You can use a %s placeholder for the description of the expected exception. E.g. "Test doesn't throw %s." will fail with the error message "Test doesn't throw an instance of foo.".

Since:

4.7

none

 public static ExpectedException none()

Returns a rule that expects no exception to be thrown (identical to behavior without this rule).

handleAssertionErrors

 @Deprecated public ExpectedException handleAssertionErrors()

Deprecated. AssertionErrors are handled by default since JUnit 4.12. Just like in JUnit <= 4.10.

This method does nothing. Don't use it.

handleAssumptionViolatedExceptions

 @Deprecated public ExpectedException handleAssumptionViolatedExceptions()

Deprecated. AssumptionViolatedExceptions are handled by default since JUnit 4.12. Just like in JUnit <= 4.10.

This method does nothing. Don't use it.

reportMissingExceptionWithMessage

 public ExpectedException reportMissingExceptionWithMessage(String message)

Specifies the failure message for tests that are expected to throw an exception but do not throw any. You can use a %s placeholder for the description of the expected exception. E.g. "Test doesn't throw %s." will fail with the error message "Test doesn't throw an instance of foo.".

Parameters:

message - exception detail message

Returns:

the rule itself

apply

 public Statement apply(Statement base, Description description)

Description copied from interface: TestRule

Modifies the method-running Statement to implement this test-running rule.

Specified by:

apply in interface TestRule

Parameters:

base - The Statement to be modified

description - A Description of the test implemented in base

Returns:

a new statement, which may be the same as base, a wrapper around base, or a completely new Statement.

expect

 public void expect(Matcher<?> matcher)

Verify that your code throws an exception that is matched by a Hamcrest matcher.

 @Test public void throwsExceptionThatCompliesWithMatcher() { NullPointerException e = new NullPointerException(); thrown.expect(is(e)); throw e; }

expect

 public void expect(Class<? extends Throwable> type)

Verify that your code throws an exception that is an instance of specific type.

 @Test public void throwsExceptionWithSpecificType() { thrown.expect(NullPointerException.class); throw new NullPointerException(); }

expectMessage

 public void expectMessage(String substring)

Verify that your code throws an exception whose message contains a specific text.

 @Test public void throwsExceptionWhoseMessageContainsSpecificText() { thrown.expectMessage("happened"); throw new NullPointerException("What happened?"); }

expectMessage

 public void expectMessage(Matcher<String> matcher)

Verify that your code throws an exception whose message is matched by a Hamcrest matcher.

 @Test public void throwsExceptionWhoseMessageCompliesWithMatcher() { thrown.expectMessage(startsWith("What")); throw new NullPointerException("What happened?"); }

expectCause

 public void expectCause(Matcher<? extends Throwable> expectedCause)

Verify that your code throws an exception whose cause is matched by a Hamcrest matcher.

 @Test public void throwsExceptionWhoseCauseCompliesWithMatcher() { NullPointerException expectedCause = new NullPointerException(); thrown.expectCause(is(expectedCause)); throw new IllegalArgumentException("What happened?", cause); }