Java JUnit Library. Types of Testing

1. Testing in Development

Let's talk about types of testing and which testing methods developers use. You will learn about the stages an application goes through before being delivered to the client and the specific tests you will need to write.

What is Testing, and Why do We Need It

Types of Testing

2. Unit Tests

In this section, we're going to dive into unit testing — you'll get the rundown on its structure in Java and the ins and outs of crafting them the right way. Setting up your IDE, importing necessary libraries, and lots of hands-on practice.

Set-Up

Test-Driven Development

Creating Unit Tests

@BeforeEach

How to Test `void` Methods

Assertions

Assertions Practice

Section 2 Summary

3. Exceptions

In this section, we will enhance our coding skills by dealing with errors that can also be caught in unit tests. When testing an application, you may come across various errors, and sometimes they should be turned into exceptions. I will explain how to catch exceptions in your code, test them, and handle them properly.

Throwing Exceptions

Try-catch structure

Handling Multiple Exceptions

Handling Exceptions Practice

Creating Exceptions

Testing Exceptions

Testing Exceptions Practice

Assertions

It's time to explore different types of assertions used in the JUnit library. You're already familiar with one of them, which is assertEquals(), used to check the equality of values, determining the test's outcome. Every other assertion works in a similar way. If such an assertion evaluates to true, the test passes; otherwise, it fails.

Let's go through different types of assertions one by one:

assertEquals: Checks the equality of two values. You are already familiar with this type of assertion, but there's another interesting feature here. We can also output a message along with the error. It looks like this:

example.java

Here's what the test with a message output will look like in case the test fails. So, if the test evaluates to false, a message will be displayed, indicating how the test should have worked.

Testing.java

Here, the isEmpty() method from the String class is being tested. You can notice that a new assertion is used here, which we will now discuss:

assertTrue: Checks that a condition is true. If the condition is true, the test passes successfully. This assertion works only with boolean variables or conditions. An example of using such a condition can be seen above;

assertNull: Checks that an object is null. If the object is null, the test passes successfully. This assertion can replace cases like assertEquals(null, actual) because it can be easily replaced with the assertNull assertion.

fail: Forcibly fails the test. It's straightforward here. I can't provide specific examples of when this might be used, but this assertion exists in the JUnit library, and I should tell you about it.

Example.java

Each of the assertions mentioned above has a counterpart. For instance, if we want to check the inequality of two values, we can use assertNotEquals, whereas assertEquals is used for checking equality.

Assertion	Purpose	Opposite
`asserEquals()`	Checks the equality of two values.	`assertNotEquals()`
`assertTrue()`	Checks that a condition is `true`.	`assertFalse()`
`assertNull()`	Checks that an object is `null`.	`assertNotNull()`
`fail()`	Forcibly fails the test.	NaN

This way, you can use their counterparts. These are the primary assertions used in JUnit, and you should know how to use each of them. In different situations, you can use different tests to make it clear to yourself and other programmers who will be reviewing your code what a particular test is checking.

1. Which assertion method in JUnit is used to verify that a condition is `true`?

2. What is the purpose of the `assertFalse` assertion in JUnit?

3. How is `assertNotEquals` used in a JUnit test case?

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Java JUnit Library. Types of Testing

Assertions

Let's go through different types of assertions one by one:

assertEquals: Checks the equality of two values. You are already familiar with this type of assertion, but there's another interesting feature here. We can also output a message along with the error. It looks like this:

example.java

Here's what the test with a message output will look like in case the test fails. So, if the test evaluates to false, a message will be displayed, indicating how the test should have worked.

Testing.java

Here, the isEmpty() method from the String class is being tested. You can notice that a new assertion is used here, which we will now discuss:

assertTrue: Checks that a condition is true. If the condition is true, the test passes successfully. This assertion works only with boolean variables or conditions. An example of using such a condition can be seen above;

assertNull: Checks that an object is null. If the object is null, the test passes successfully. This assertion can replace cases like assertEquals(null, actual) because it can be easily replaced with the assertNull assertion.

Example.java

Assertion	Purpose	Opposite
`asserEquals()`	Checks the equality of two values.	`assertNotEquals()`
`assertTrue()`	Checks that a condition is `true`.	`assertFalse()`
`assertNull()`	Checks that an object is `null`.	`assertNotNull()`
`fail()`	Forcibly fails the test.	NaN

1. Which assertion method in JUnit is used to verify that a condition is `true`?

2. What is the purpose of the `assertFalse` assertion in JUnit?

3. How is `assertNotEquals` used in a JUnit test case?

Все було зрозуміло?

Секція 2. Розділ 6