Gain insights into configuring and utilizing JUnit 5 for Java unit testing. Learn about writing effective unit tests, integrating assertions, assumptions, parameterized tests, and their significance.

Junit 5 is the most popular and widely used Java unit testing framework. In this course, you will learn step by step, how to configure and use JUnit 5 testing framework. This course will teach you how to write unit tests with JUnit 5, covering topics like why unit tests are important, the structure of good unit tests, assertions, assumptions and parameterized tests and more.

Java Unit Testing with JUnit 5

# assertTrue() method ###

Assertions API provide static `assertTrue()` method. This method helps us in validating that the actual value supplied to it is `true`.

- If the actual value is `true` then test case will pass.
- If the actual value is `not true` then test case will fail.


There are basically six useful overloaded methods for assertTrue:-

public static void assertTrue(boolean condition)
  
public static void assertTrue(boolean condition, String message)

public static void assertTrue(boolean condition, Supplier<String> messageSupplier)

public static void assertTrue(BooleanSupplier booleanSupplier)
  
public static void assertTrue(BooleanSupplier booleanSupplier, String message)
  
public static void assertTrue(BooleanSupplier booleanSupplier, Supplier<String> messageSupplier)

# Demo ###

Let's look into the usage of the above methods:- 

package io.educative.junit5;

import static org.junit.jupiter.api.Assertions.assertTrue;

import org.junit.jupiter.api.Test;

public class AssertTrueDemo {

	@Test
	public void testAssertTrueWithTrueCondition() {
		boolean trueValue = true;
		assertTrue(trueValue);
	}
	
	@Test
	public void testAssertTrueWithFalseCondition() {
		boolean falseValue = false;
		assertTrue(falseValue);
	}
	
	@Test
	public void testAssertTrueWithFalseConditionAndMessage() {
		boolean falseValue = false;
		assertTrue(falseValue, "The actual value is false");
	}
	
	@Test
	public void testAssertTrueWithFalseConditionAndMessageSupplier() {
		boolean falseValue = false;
		assertTrue(falseValue, () -> "The actual value is false");
	}
	
	@Test
	public void testAssertTrueWithBooleanSupplier() {
		boolean trueValue = true;
		assertTrue(() -> trueValue);
	}
	
	@Test
	public void testAssertTrueWithBooleanSupplierAndMessage() {
		boolean falseValue = false;
		assertTrue(() -> falseValue, "The actual value is false");
	}
	
	@Test
	public void testAssertTrueWithBooleanSupplierAndMessageSupplier() {
		boolean falseValue = false;
		assertTrue(() -> falseValue, () -> "The actual value is false");
	}
}

> You can perform code changes to above code widget, run and practice different outcomes.

# Explanation - ###

In AssertTrueDemo class there are 7 @Test methods. These 7 methods demonstrate the working of the above 6 overloaded methods of `assertTrue`:- 

1. `testAssertTrueWithTrueCondition()` - It asserts the boolean value provided to `assertTrue()` method. Here, the actual value passed to it is `true`. Thus, it passes the Junit test case because `assertTrue` asserts that value passed to it should be true.  

2. `testAssertTrueWithFalseCondition()` - It asserts the boolean value provided to `assertTrue()` method. Here, actual value passed to it is `false`. Thus, it fails the Junit test case with `AssertionFailedError: `expected: &lt;true&gt; but was: &lt;false&gt; because value passed to `assertTrue` method is `false.`

3. `testAssertTrueWithFalseConditionAndMessage` - It asserts the boolean value provided to `assertTrue()` method. Here, actual value passed to it is `false`. Thus, it fails the Junit test case with `AssertionFailedError:` The actual value is false ==> expected: &lt;true&gt; but was: &lt;false&gt; because value passed to `assertTrue` method is `false.` It gives `AssertionFailedError` followed `String message` we provide to assertTrue() method.<p>  

4. `testAssertTrueWithFalseConditionAndMessageSupplier` - It asserts the boolean value provided to `assertTrue()` method. Here, actual value passed to it is `false`. Thus, it fails the Junit test case with `AssertionFailedError:` The actual value is false ==> expected: &lt;true&gt; but was: &lt;false&gt; because value passed to `assertTrue` method is `false.` It gives `AssertionFailedError` followed by lazily evaluates `String message` we provide to assertTrue() method, as lambda expression.<p> 

5. `testAssertTrueWithBooleanSupplier()` - It asserts the boolean value provided to `assertTrue()` method through BooleanSupplier functional interface. Here, actual value passed to it is `true`. Thus, it passes the JUnit test case because `assertTrue` asserts that value passed to it should be true.
6. `testAssertTrueWithBooleanSupplierAndMessage` - It asserts the boolean value provided to `assertTrue()` method through BooleanSupplier functional interface. Here, actual value passed to it is `false`. Thus, it fails the Junit test case with `AssertionFailedError:` The actual value is false ==> expected: &lt;true&gt; but was: &lt;false&gt; because value passed to `assertTrue` method is `false.` It gives `AssertionFailedError` followed `String message` we provide to assertTrue() method.<p>
7. `testAssertTrueWithBooleanSupplierAndMessageSupplier` - It asserts the boolean value provided to `assertTrue()` method through BooleanSupplier functional interface. Here, actual value passed to it is `false`. Thus, it fails the Junit test case with `AssertionFailedError:` The actual value is false ==> expected: &lt;true&gt; but was: &lt;false&gt; because value passed to `assertTrue` method is `false.` It gives `AssertionFailedError` followed by lazily evaluates `String message` we provide to assertTrue() method, as lambda expression.<p>

This lesson demonstrates how to use assertTrue method in JUnit 5 to assert test conditions. 

Getting Started

Assertions in Junit 5

Junit 5 Test Lifecycle Callbacks

Display Names

Dependency Injection for Constructors and Methods

Assumptions in Junit 5

Disable or Enable Tests in Junit 5

Nested Tests in Junit 5

JUnit 5 Integration with Maven

Parameterized Tests in Junit 5

Repeated Tests in Junit 5

Appendix

assertTrue() method

assertTrue() method