Junit: Create custom rules

You can create a custom rule by implementing 'TestRule' interface.

For example, I created CustomLogger rule, it logs the test case details, before executing actual test case.

CustomLogger.java

package com.sample.customrules;

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

public class CustomLogger implements TestRule {

 @Override
 public Statement apply(Statement base, Description description) {
  return new Statement() {
   @Override
   public void evaluate() throws Throwable {
    System.out.println(description.getDisplayName());
    base.evaluate();
   }
  };
 }

}

TestApp.java

package com.sample.test;

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

import com.sample.customrules.CustomLogger;

public class TestApp {
 @Rule
 public CustomLogger logger = new CustomLogger();
 
 @Test
 public void testCase1() {
  System.out.println("Executing testCase1");
 }

 @Test
 public void testCase2() {
  System.out.println("Executing testCase2");
 }

 
}

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

testCase1(com.sample.test.TestApp)

Executing testCase1

testCase2(com.sample.test.TestApp)

Executing testCase2

Test Case Execution timer
Calculate and print the execution time of a test case.

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(description.getMethodName() + " takes " + (time2-time1) + " milliseconds");
   }
  };
 }
}

TestApp.java

package com.sample.test;

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

import com.sample.customrules.TestCaseExecutionTimer;

public class TestApp {
 @Rule
 public 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);
 }

}

Run ‘TestApp.java’, you can able to see below messages in console.

Executing testCase1

testCase1 takes 501 milliseconds

Executing testCase2

testCase2 takes 100 milliseconds

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