Test class to Test a class with Multiple Static Methods using PowerMockito

StaticMethodsTest.java

/* File:    StaticMethodsTest.java
 * Created: 2018-05-03
 * Author:  Sabbir Manandhar
 *
 * Copyright (c) 2018 Hogwarts.
 */

package com.worldlingo;

import junit.framework.Assert;
import org.junit.Test;
import org.junit.runner.RunWith;
import org.mockito.Mockito;
import org.powermock.api.mockito.PowerMockito;
import org.powermock.core.classloader.annotations.PrepareForTest;
import org.powermock.modules.junit4.PowerMockRunner;

/**
 * JUnit test cases using PowerMockito for the Static Methods in a Class
 *
 * @author Sabbir Manandhar
 * @version 1.0
 */
@RunWith(PowerMockRunner.class)
@PrepareForTest({TestClass.class})
public class StaticMethodsTest {

  /**
   * PowerMockito.mockStatic(); mocks all the static methods in a class
   * So even you explicitly define mocked return for the static method,
   * execution of the method in the test will still be mocked and won't execute
   * its actual code. Instead it will return null (or appropriate value) if it
   * has return value.
   *
   * @throws Exception
   */
  @Test
  public void test() throws Exception {
    PowerMockito.mockStatic(TestClass.class);
    PowerMockito.doReturn("TOM").when(TestClass.class, "toUpperCase", Mockito.anyString());

    String result1 = TestClass.toUpperCase("I am the king");
    String result2 = TestClass.toLowerCase("I am the king");
    String result3 = TestClass.alterWords("I am the king");
    Assert.assertEquals("TOM", result1);
    Assert.assertNull(result2);
    Assert.assertNull(result3);
  } // test

  //-----------------------------------------------------------------------------------------------

  /**
   * Similar to first test method
   * All static methods will be mocked
   * Here return value for each static methods are defined, and results are as expected
   *
   * @throws Exception
   */
  @Test
  public void test2() throws Exception {
    PowerMockito.mockStatic(TestClass.class);
    PowerMockito.doReturn("TOM").when(TestClass.class, "toUpperCase", Mockito.anyString());
    PowerMockito.doReturn("marvolo").when(TestClass.class, "toLowerCase", Mockito.anyString());
    PowerMockito.doReturn("VoLdEmOrT").when(TestClass.class, "alterWords", Mockito.anyString());

    String result1 = TestClass.toUpperCase("I am the king");
    String result2 = TestClass.toLowerCase("I am the king");
    String result3 = TestClass.alterWords("I am the king");
    Assert.assertEquals("TOM", result1);
    Assert.assertEquals("marvolo", result2);
    Assert.assertEquals("VoLdEmOrT", result3);
  } // test2

  //------------------------------------------------------------------------------------------------

  /**
   * Mock individual Static method
   * Here TestClass.toUpperCase() and TestClass.toLowerCase() are mocked
   * but TestClass.alterWords() is not
   * So TestClass.alterWords() will actually execute the original code which
   * in turn invokes the methods toUpperCase() and toLowerCase(). Since these
   * are mocked, mocked results will be returned.
   *
   * @throws Exception
   */
  @Test
  public void test3() throws Exception {
    PowerMockito.spy(TestClass.class);
    PowerMockito.doReturn("TOM").when(TestClass.class, "toUpperCase", Mockito.anyString());
    PowerMockito.doReturn("marvolo").when(TestClass.class, "toLowerCase", Mockito.anyString());

    String result1 = TestClass.toUpperCase("I am the king");
    String result2 = TestClass.toLowerCase("I am the king");
    String result3 = TestClass.alterWords("I am the king");
    Assert.assertEquals("TOM", result1);
    Assert.assertEquals("marvolo", result2);
    Assert.assertEquals("TOM marvolo TOM marvolo ", result3);
  } // test3
} // StaticMethodsTest

//-----------------------------------------------------------------------------------------

/**
 * Test class with Static Methods
 */
class TestClass {

  public static String toUpperCase(String input) {
    return input.toUpperCase();
  } // toUpperCase

  //---------------------------------------------------------------------------------------

  public static String toLowerCase(String input) {
    return input.toLowerCase();
  } // toLowerCase

  //---------------------------------------------------------------------------------------

  public static String alterWords(String input) {
    String[] comps = input.split(" ");
    StringBuilder sb = new StringBuilder();
    boolean alt = true;
    for (String comp : comps) {
      if (alt) {
        sb.append(toUpperCase(comp)).append(" ");
      } else {
        sb.append(toLowerCase(comp)).append(" ");
      }
      alt = !alt;
    }
    return sb.toString();
  } // alterWords

  //----------------------------------------------------------------------------------------

} // TestClass