JUnit Timeout TestRule Example

Using TestRule one can alter the behavior of a test method. In this article, we will see an example of JUnit’s Timeout rule that makes sure that each test is run in a time limit manner. Timeout rule is applied to all test methods where each test is run in a separate thread in a time bound manner. If the test didn’t finish within the specified time, a TestTimedOutException will be thrown.

Internally the statement that executes the test is wrapped around the another statement that in turn runs the the original statement in a separate thread and waits for the result using the specified timeout value.

Below is a test class that runs the test aTestHanging, will automatically fail after waiting for 5 secs. We define the timeout rule using a non-static, public instance variable of type Timeout. A timeout instance is created using the factory method Timeout.millis() where we pass the timeout in mill seconds.

TimeoutExample:

package com.javarticles.junit;

import org.junit.After;
import org.junit.AfterClass;
import org.junit.Rule;
import org.junit.Test;
import org.junit.rules.Timeout;

public class TimeoutExample {
    @Rule
    public final Timeout timeOut = Timeout.millis(5000);
    
    @Test
    public void aTestHanging() {   
        System.out.println("Start test");
        for(;;){}
    }    
    
    @After
    public void afterTest() {
        System.out.println("After test - wont be called due to timeout");
    }
    
    @AfterClass
    public static void done() {
        System.out.println("Test finished due to timeout");
    }
}

As you can see the test doesn’t finish so the @After test method is not run.

Output:

Befor class
Before test
Start test
After class

Test fails with timeout exception.

Error Trace:

org.junit.runners.model.TestTimedOutException: test timed out after 5000 milliseconds
	at com.javarticles.junit.TimeoutExample.aTestHanging(TimeoutExample.java:18)
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
	at java.lang.reflect.Method.invoke(Method.java:483)
	at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:50)
	at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:12)
	at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:47)
	at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:17)
	at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:26)
	at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:27)
	at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:298)
	at org.junit.internal.runners.statements.FailOnTimeout$CallableStatement.call(FailOnTimeout.java:292)
	at java.util.concurrent.FutureTask.run(FutureTask.java:266)
	at java.lang.Thread.run(Thread.java:745)

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This was an example about JUnit Timeout TestRule.