'Using junit @Rule, expectCause() and hamcrest matchers

I have a test:

@Rule
public ExpectedException thrown = ExpectedException.none();
...
@Test
public void testMethod()
{
    final String error = "error message";
    Throwable expectedCause = new IllegalStateException(error);
    thrown.expectCause(org.hamcrest.Matchers.<Throwable>equalTo(expectedCause));
    someServiceThatTrowsException.foo();
}

When run via mvn the test method, I'm getting the error:

java.lang.NoSuchMethodError: org.junit.rules.ExpectedException.expectCause(Lorg/hamcrest/Matcher;)V

Test compiles fine.

Please help me, cannot understand how to test the cause of the exception?

javaunit-testingmavenjunit


Solution 1:[1]

Try it this way:

@Rule public ExpectedException thrown = ExpectedException.none();

@Test public void testMethod() throws Throwable {
    final String error = "error message";
    Throwable expectedCause = new IllegalStateException(error);
    thrown.expectCause(IsEqual.equalTo(expectedCause));
    throw new RuntimeException(expectedCause);
}

Consider not to check against the cause by equals but by IsInstanceOf and / or comapring the exception message if necessary. Comparing the cause by equals check the stacktrace as well, which may be more than you would like to test / check. Like this for example:

@Rule public ExpectedException thrown = ExpectedException.none();

@Test public void testMethod() throws Throwable {
    final String error = "error message";
    thrown.expectCause(IsInstanceOf.<Throwable>instanceOf(IllegalStateException.class));
    thrown.expectMessage(error);
    throw new RuntimeException(new IllegalStateException(error));
}

Solution 2:[2]

A little bit more briefly with static imports and checking both the class and the message of the cause exception: 

import static org.hamcrest.Matchers.allOf;
import static org.hamcrest.Matchers.hasProperty;
import static org.hamcrest.Matchers.instanceOf;
import static org.hamcrest.Matchers.is;
import static org.junit.Assert.assertThat;

@Test
public void testThatThrowsNiceExceptionWithCauseAndMessages(){

     expectedException.expect(RuntimeException.class );
     expectedException.expectMessage("Exception message");                                           
     expectedException.expectCause(allOf(instanceOf(IllegalStateException.class),
                                        hasProperty("message", is("Cause message"))) );

     throw new RuntimeException("Exception message", new IllegalStateException("Cause message"));
}

You could even use the hasProperty matcher to assert nested causes or to test the "getLocalizedMessage" method.

Solution 3:[3]

You can use a custom matcher as described here (http://www.javacodegeeks.com/2014/03/junit-expectedexception-rule-beyond-basics.html) to test for the cause of an exception.

Custom matcher

private static class CauseMatcher extends TypeSafeMatcher<Throwable> {

    private final Class<? extends Throwable> type;
    private final String expectedMessage;

    public CauseMatcher(Class<? extends Throwable> type, String expectedMessage) {
        this.type = type;
        this.expectedMessage = expectedMessage;
    }

    @Override
    protected boolean matchesSafely(Throwable item) {
        return item.getClass().isAssignableFrom(type)
                && item.getMessage().contains(expectedMessage);
    }

    @Override
    public void describeTo(Description description) {
        description.appendText("expects type ")
                .appendValue(type)
                .appendText(" and a message ")
                .appendValue(expectedMessage);
    }
}

Test case

@Rule
public ExpectedException thrown = ExpectedException.none();

@Test
public void verifiesCauseTypeAndAMessage() {
    thrown.expect(RuntimeException.class);
    thrown.expectCause(new CauseMatcher(IllegalStateException.class, "Illegal state"));

    throw new RuntimeException("Runtime exception occurred",
            new IllegalStateException("Illegal state"));
}

Solution 4:[4]

It's JUnit version problem.

ExpectedException.expectCause() is since 4.11.

No such method in 4.10 or lower.

You should ensure your runtime JUnit version >= 4.11, same as your compile version.

Solution 5:[5]

To summarize all.

With JUnit 4 ( hamcrest 1.3 , and be careful, JUnit 4 depend on hamcrest-core which not include org.hamcrest.beans package)

So, you need to import:

<dependency>
  <groupId>org.hamcrest</groupId>
  <artifactId>hamcrest-all</artifactId>
  <version>1.3</version>
  <scope>test</scope>
</dependency>

Code:

import static org.hamcrest.CoreMatchers.*;
import static org.hamcrest.beans.HasPropertyWithValue.hasProperty;

@Rule
public ExpectedException expectedException = ExpectedException.none();

@Test
public void testThatThrowsNiceExceptionWithCauseAndMessages(){

  expectedException.expect(RuntimeException.class );
  expectedException.expectMessage("Exception message");                                           
  expectedException.expectCause(
    allOf(
      isA(IllegalStateException.class),
      hasProperty("message", is("Cause message"))
    )
  );

  throw 
    new RuntimeException("Exception message", 
      new IllegalStateException("Cause message"));
}

Solution 6:[6]

Normally I like more the following construction:

expectedException.expectCause(isA(NullPointerException.class));

Solution 7:[7]

The any(Class<T>) matcher from hamcrest works nicely:

@Rule
public ExpectedException thrown = ExpectedException.none();
...
@Test
public void testMethod()
{
    thrown.expect(RuntimeException.class);
    thrown.expectCause(org.hamcrest.Matchers.any(IllegalStateException.class));
}

Solution 8:[8]

Import

<dependency>
  <groupId>it.ozimov</groupId>
  <artifactId>java7-hamcrest-matchers</artifactId>
  <version>1.3.0</version>
  <scope>test</scope>
</dependency>

And then:

@Rule
public ExpectedException thrown = ExpectedException.none();
...
@Test
public void testMethod()
{
    final String errorMessage = "error message";
    Class<? extends Throwable> expectedCause = IllegalStateException.class;
    thrown.expectCause(ExpectedException.exceptionWithMessage(expectedCause, errorMessage));
    someServiceThatTrowsException.foo();
}

It works also with subtype of the cause. In other solutions I observed that they accept a supertype, that is wrong in my opinion.

Message must be equal or contained in the cause's error message.

Solution 9:[9]

You can do this entirely with built-in matchers org.hamcrest.Matchers.instanceOf and org.junit.internal.matchers.ThrowableMessageMatcher.hasMessage:

import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.ExpectedException;

import static org.hamcrest.Matchers.equalTo;
import static org.hamcrest.Matchers.instanceOf;
import static org.hamcrest.Matchers.both;
import static org.junit.internal.matchers.ThrowableMessageMatcher.hasMessage;

public class temp {
    @Rule
    public ExpectedException expectedException = ExpectedException.none();

    @Test
    public void youCannotDivideByZero() {
        expectedException.expect(RuntimeException.class);
        expectedException.expectMessage(equalTo("Division exception"));
        expectedException.expectCause(both(hasMessage(equalTo("/ by zero"))).and(instanceOf(ArithmeticException.class)));
        divide(1, 0);
    }

    private float divide(int first, int second) {
        try {
            return first / second;
        } catch(ArithmeticException e) {
            throw new RuntimeException("Division exception", e);
        }
    }
}

Solution 10:[10]

The answers so far all use the deprecated method - ExpectedException.none().

This should now be done with assertThrows, which returns the actual exception, which can then be tested in the usual ways.

This gives a lot more expressive power to the test case writer as the exception is not required to be the end of the test case.


@Test
public void testWithIOException() {
    // ...
    IOException exception = assertThrows(IOException.class, 
        () -> someServiceThatThrowsException.foo());

    assertTrue(exception.getMessage().contains("my error message"));
}

many thanks to: https://jsparrow.github.io/rules/replace-j-unit-expected-exception.html#code-changes

Solution 11:[11]

Example of verifying the message and cause of a thrown exception for Kotlin language:

@get:Rule
val exceptionRule: ExpectedException = ExpectedException.none()

@Test
fun `test method`() {
    exceptionRule.expect(NestedServletException::class.java)
    exceptionRule.expectMessage("error msg")
    exceptionRule.expectCause(instanceOf(IllegalStateException::class.java))
    // ...

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