JUnit 5 assertTrue Example

JUnit 5 Tutorial

In this article, we will learn about assertTrue() static method which belongs to JUnit 5 org.junit.jupiter.api.Assertions Class. Note that in JUnit 5 all JUnit 4 assertion methods are moved to org.junit.jupiter.api.Assertions class.

There are many overloaded version of assertTrue() methods present in org.junit.jupiter.api.Assertions class.

Let me list out tools and technologies that I have used to develop JUnit 5 assertTrue Example.

Tools and Technologies Used

Eclipse photon (only this eclipse version supports JUnit 5)
Maven
JUnit 5
JDK 8 or later

assertTrue() method asserts that a condition is true. If it isn't it throws an AssertionError without a message.

assertTrue() method Example

In this example, first we will create a logical isEmpty()_ and isBlank methods and then we will test these methods using JUnit 5 assertTrue method.

public static boolean isEmpty(final CharSequence cs) {
 return cs == null || cs.length() == 0;
}

public static boolean isBlank(final CharSequence cs) {
 int strLen;
 if (cs == null || (strLen = cs.length()) == 0) {
  return true;
 }
 for (int i = 0; i < strLen; i++) {
  if (!Character.isWhitespace(cs.charAt(i))) {
   return false;
  }
 }
 return true;
}

Let's write a JUnit test for the above methods with different scenarios:

@Test
public void isEmptyTest() {
 assertTrue(isEmpty(null));
 assertTrue(isEmpty(""));
 assertFalse(isEmpty(" "));
 assertFalse(isEmpty("bob"));
 assertFalse(isEmpty("  bob  "));
}

@Test
public void isBlankTest() {
 assertTrue(isBlank(null));
 assertTrue(isBlank(""));
 assertTrue(isBlank(" "));
 assertFalse(isBlank("bob"));
 assertFalse(isBlank("  bob  "));
}

Complete Program for Reference

import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertTrue;

import org.junit.jupiter.api.Test;

public class JUnit5AssertTrueExample {
 
 public static boolean isEmpty(final CharSequence cs) {
  return cs == null || cs.length() == 0;
 }

 public static boolean isBlank(final CharSequence cs) {
  int strLen;
  if (cs == null || (strLen = cs.length()) == 0) {
   return true;
  }
  for (int i = 0; i < strLen; i++) {
   if (!Character.isWhitespace(cs.charAt(i))) {
    return false;
   }
  }
  return true;
 }

 @Test
 public void isEmptyTest() {
  assertTrue(isEmpty(null));
  assertTrue(isEmpty(""));
  assertFalse(isEmpty(" "));
  assertFalse(isEmpty("bob"));
  assertFalse(isEmpty("  bob  "));
 }

 @Test
 public void isBlankTest() {
  assertTrue(isBlank(null));
  assertTrue(isBlank(""));
  assertTrue(isBlank(" "));
  assertFalse(isBlank("bob"));
  assertFalse(isBlank("  bob  "));
 }
}