Junit: @ClassRule annotation

It is like @Rule annotation, only difference is, this rule only applicable to static fields, methods.

For example, below example calculates the execution time of all the test cases.

TestCaseExecutionTimer.java

package com.sample.customrules;

import org.junit.rules.TestRule;
import org.junit.runner.Description;
import org.junit.runners.model.Statement;

public class TestCaseExecutionTimer implements TestRule{
 @Override
 public Statement apply(Statement base, Description description) {
  return new Statement() {
   @Override
   public void evaluate() throws Throwable {
    long time1 = System.currentTimeMillis();
    base.evaluate();
    long time2 = System.currentTimeMillis();
    
    System.out.println("Test cases in " + description.getClassName() + " takes " + (time2-time1) + " milliseconds");
   }
  };
 }
}

TestApp.java

package com.sample.test;

import org.junit.ClassRule;
import org.junit.Test;

import com.sample.customrules.TestCaseExecutionTimer;

public class TestApp {
 @ClassRule
 public static TestCaseExecutionTimer timer = new TestCaseExecutionTimer();

 @Test
 public void testCase1() throws InterruptedException {
  System.out.println("Executing testCase1");
  Thread.sleep(500);
 }

 @Test
 public void testCase2() throws InterruptedException {
  System.out.println("Executing testCase2");
  Thread.sleep(100);
 }

}

When you ran TestApp.java, you can able to see below messages in console.

Executing testCase1

Executing testCase2

Test cases in com.sample.test.TestApp takes 609 milliseconds

Now let’s combine both @Rule and @ClassRule to get each test case execution time and cumulative execution time.

TestCaseExecutionTimer.java

package com.sample.customrules;

import org.junit.rules.TestRule;
import org.junit.runner.Description;
import org.junit.runners.model.Statement;

public class TestCaseExecutionTimer implements TestRule {
 @Override
 public Statement apply(Statement base, Description description) {
  return new Statement() {
   @Override
   public void evaluate() throws Throwable {
    long time1 = System.currentTimeMillis();
    base.evaluate();
    long time2 = System.currentTimeMillis();

    if (description.getMethodName() != null) {
     System.out.println(description.getMethodName() + " takes " + (time2 - time1) + " milliseconds");
    } else {
     System.out.println("Test cases in " + description.getClassName() + " takes " + (time2 - time1)
       + " milliseconds");
    }

   }
  };
 }
}

TestApp.java

package com.sample.test;

import org.junit.ClassRule;
import org.junit.Rule;
import org.junit.Test;

import com.sample.customrules.TestCaseExecutionTimer;

public class TestApp {
 @ClassRule
 public static TestCaseExecutionTimer CumulativeTimer = new TestCaseExecutionTimer();

 @Rule
 public TestCaseExecutionTimer testCaseTimer = new TestCaseExecutionTimer();
 
 @Test
 public void testCase1() throws InterruptedException {
  System.out.println("Executing testCase1");
  Thread.sleep(500);
 }

 @Test
 public void testCase2() throws InterruptedException {
  System.out.println("Executing testCase2");
  Thread.sleep(100);
 }

}

When you ran TestApp.java, you can able to see below messages in console.

Executing testCase1

testCase1 takes 501 milliseconds

Executing testCase2

testCase2 takes 100 milliseconds

Test cases in com.sample.test.TestApp takes 606 milliseconds

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