Class ExpectedException
- java.lang.Object
- org.junit.rules.ExpectedException
- All Implemented Interfaces:
TestRule
public class ExpectedException extends Object implements TestRule
TheExpectedException
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 (seethrowsNothing()
). 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
AssumptionViolatedException
s for indicating that a test provides no useful information. (SeeAssume
for more information.) You have to callassume
methods before you set expectations of theExpectedException
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
AssertionError
s for indicating that a test is failing. You have to callassert
methods before you set expectations of theExpectedException
rule, if they should be handled by the framework. E.g. the following test fails because of theassertTrue
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
Method Summary
All Methods Static Methods Instance Methods Concrete Methods Deprecated Methods Modifier and Type Method Description Statement
apply(Statement base, Description description)
Modifies the method-runningStatement
to implement this test-running rule.void
expect(Class<? extends Throwable> type)
Verify that your code throws an exception that is an instance of specifictype
.void
expect(Matcher<?> matcher)
Verify that your code throws an exception that is matched by a Hamcrest matcher.void
expectCause(Matcher<? extends Throwable> expectedCause)
Verify that your code throws an exception whose cause is matched by a Hamcrest matcher.void
expectMessage(String substring)
Verify that your code throws an exception whose message contains a specific text.void
expectMessage(Matcher<String> matcher)
Verify that your code throws an exception whose message is matched by a Hamcrest matcher.ExpectedException
handleAssertionErrors()
Deprecated.AssertionErrors are handled by default since JUnit 4.12.ExpectedException
handleAssumptionViolatedExceptions()
Deprecated.AssumptionViolatedExceptions are handled by default since JUnit 4.12.static ExpectedException
none()
Returns a rule that expects no exception to be thrown (identical to behavior without this rule).ExpectedException
reportMissingExceptionWithMessage(String message)
Specifies the failure message for tests that are expected to throw an exception but do not throw any.
Method Detail
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-runningStatement
to implement this test-running rule.- Specified by:
apply
in interfaceTestRule
- Parameters:
base
- TheStatement
to be modifieddescription
- ADescription
of the test implemented inbase
- Returns:
- a new statement, which may be the same as
base
, a wrapper aroundbase
, 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 specifictype
.@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); }