org.junit.rules.ExpectedException Maven / Gradle / Ivy
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package org.junit.rules;
import static java.lang.String.format;
import static org.hamcrest.CoreMatchers.containsString;
import static org.hamcrest.CoreMatchers.instanceOf;
import static org.junit.Assert.assertThat;
import static org.junit.Assert.fail;
import static org.junit.internal.matchers.ThrowableCauseMatcher.hasCause;
import static org.junit.internal.matchers.ThrowableMessageMatcher.hasMessage;
import org.hamcrest.Matcher;
import org.hamcrest.StringDescription;
import org.junit.AssumptionViolatedException;
import org.junit.runners.model.Statement;
/**
* The {@code 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 {@code ExpectedException} rule to your test.
* This doesn't affect your existing tests (see {@code 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: {@link #expectMessage(String)}
* - The exception's message complies with a Hamcrest matcher: {@link #expectMessage(Matcher)}
* - The exception's cause complies with a Hamcrest matcher: {@link #expectCause(Matcher)}
* - The exception itself complies with a Hamcrest matcher: {@link #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 {@link AssumptionViolatedException}s for indicating that a test
* provides no useful information. (See {@link org.junit.Assume} for more
* information.) You have to call {@code assume} methods before you set
* expectations of the {@code 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 {@link AssertionError}s for indicating that a test is failing. You
* have to call {@code assert} methods before you set expectations of the
* {@code ExpectedException} rule, if they should be handled by the framework.
* E.g. the following test fails because of the {@code 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 {@link #reportMissingExceptionWithMessage(String)}. You
* can use a {@code %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
*/
public class ExpectedException implements TestRule {
/**
* Returns a {@linkplain TestRule rule} that expects no exception to
* be thrown (identical to behavior without this rule).
*/
public static ExpectedException none() {
return new ExpectedException();
}
private final ExpectedExceptionMatcherBuilder matcherBuilder = new ExpectedExceptionMatcherBuilder();
private String missingExceptionMessage= "Expected test to throw %s";
private ExpectedException() {
}
/**
* This method does nothing. Don't use it.
* @deprecated AssertionErrors are handled by default since JUnit 4.12. Just
* like in JUnit <= 4.10.
*/
@Deprecated
public ExpectedException handleAssertionErrors() {
return this;
}
/**
* This method does nothing. Don't use it.
* @deprecated AssumptionViolatedExceptions are handled by default since
* JUnit 4.12. Just like in JUnit <= 4.10.
*/
@Deprecated
public ExpectedException handleAssumptionViolatedExceptions() {
return this;
}
/**
* Specifies the failure message for tests that are expected to throw
* an exception but do not throw any. You can use a {@code %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.".
*
* @param message exception detail message
* @return the rule itself
*/
public ExpectedException reportMissingExceptionWithMessage(String message) {
missingExceptionMessage = message;
return this;
}
public Statement apply(Statement base,
org.junit.runner.Description description) {
return new ExpectedExceptionStatement(base);
}
/**
* 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;
* }
*/
public void expect(Matcher matcher) {
matcherBuilder.add(matcher);
}
/**
* Verify that your code throws an exception that is an
* instance of specific {@code type}.
* @Test
* public void throwsExceptionWithSpecificType() {
* thrown.expect(NullPointerException.class);
* throw new NullPointerException();
* }
*/
public void expect(Class type) {
expect(instanceOf(type));
}
/**
* 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?");
* }
*/
public void expectMessage(String substring) {
expectMessage(containsString(substring));
}
/**
* 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?");
* }
*/
public void expectMessage(Matcher matcher) {
expect(hasMessage(matcher));
}
/**
* 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);
* }
*/
public void expectCause(Matcher expectedCause) {
expect(hasCause(expectedCause));
}
private class ExpectedExceptionStatement extends Statement {
private final Statement next;
public ExpectedExceptionStatement(Statement base) {
next = base;
}
@Override
public void evaluate() throws Throwable {
try {
next.evaluate();
} catch (Throwable e) {
handleException(e);
return;
}
if (isAnyExceptionExpected()) {
failDueToMissingException();
}
}
}
private void handleException(Throwable e) throws Throwable {
if (isAnyExceptionExpected()) {
assertThat(e, matcherBuilder.build());
} else {
throw e;
}
}
private boolean isAnyExceptionExpected() {
return matcherBuilder.expectsThrowable();
}
private void failDueToMissingException() throws AssertionError {
fail(missingExceptionMessage());
}
private String missingExceptionMessage() {
String expectation= StringDescription.toString(matcherBuilder.build());
return format(missingExceptionMessage, expectation);
}
}