Hi! My name is Viacheslav Aksenov and I am a backend developer specializing in developing complex backend systems in Java and Kotlin. Also, I write a lot of code for myself, which you can find on my GitHub: [https://github.com/v-aksenov](https://github.com/v-aksenov?ref=hackernoon.com)

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If you don’t write tests for your code, then I'll tell you why tests are worth every minute you invest in them. In this article, you can find tips to help you get started writing tests, and I’ll tell you how to do it.

## Why Test Writing Is Very Important

There are 4 main benefits that you get when you begin to write tests for your code:

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1. Improved code quality: By writing tests, you can ensure that your code is working correctly and that any changes you make do not break existing functionality. This can help you catch bugs early on and prevent them from becoming major issues down the line.

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2. Faster development: Automated tests can be run quickly and consistently, which can save you time and effort when developing your application. This can be especially useful when making changes to your code, as you can quickly run your tests to ensure that your changes have not introduced any new bugs.

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3. Easier debugging: If you encounter a problem with your application, having a suite of tests can make it easier to identify the source of the issue. By running your tests, you can quickly determine which part of your code is causing the problem and focus your efforts on fixing it.

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4. Increased confidence: Writing tests can give you confidence in your code and in the changes you make to it. This can be especially useful when working on a large, complex application, where it can be difficult to know for sure that your code is correct.

## Okay, I Believe You, but How Do I Start?

There are several best practices that can be followed when testing web applications:

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* Writing automated tests: Automated tests are essential for ensuring that your application is working correctly and that any changes you make do not break existing functionality. Automated tests can be run quickly and consistently, making them a valuable tool for catching bugs and ensuring that your application is of high quality.

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* Using a test-driven development approach: Test-driven development (TDD) is a software development methodology in which tests are written before the implementation code. This helps ensure that the code is written to satisfy the requirements of the tests and that the tests are comprehensive and effective.

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* Writing unit tests: Unit tests are small, focused tests that test individual components or units of your application in isolation. This helps ensure that each component is working correctly, and makes it easier to identify the source of any problems that may arise.

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* Writing integration tests: Integration tests test how different components of your application work together. This is important because it helps ensure that your application is functional and that different parts of your code are compatible with one another.

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* Using a mocking framework: Mocking frameworks can be used to simulate the behavior of external dependencies, such as databases or web services, in your tests. This can be useful for testing how your application responds to different scenarios without having to actually set up the dependencies.

## Did You Say TDD? What is That?

Test-driven development (TDD) is a software development methodology in which tests are written for a new piece of code before the code itself is written. The tests are used to define the desired behavior of the code, and the code is then implemented to pass the tests.

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The TDD process typically follows the following steps:

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1. Write a test for a small, specific behavior of the code.
2. Run the test and verify that it fails, since the code has not been implemented yet.
3. Write the minimum amount of code needed to make the test pass.
4. Run the test again and verify that it passes.
5. Refactor the code to improve its design and structure, without changing its behavior.
6. Repeat the process for the next small, specific behavior of the code.

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The goal of TDD is to produce well-designed, well-tested code that is easy to maintain and extend. By writing tests before writing the code, you can ensure that the code satisfies the requirements and behaves as expected. 

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This can help you catch and fix bugs early in the development process, and can also help you design your code in a more modular and reusable way.

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TDD is often used in combination with other software development methodologies, such as agile development or extreme programming.

## How Do I Write Unit Tests?

It is not a very difficult question. When you figured out that you need to write a unit test, but don’t know how, you can follow these steps:

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1. Identify the unit of code that you want to test. A unit test typically tests a small, specific piece of code, such as a single method or function.

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2. Write a test case for the unit of code. A test case is a set of instructions that specifies how the code should behave and what the expected result should be.

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3. Set up the necessary preconditions for the test. This might involve creating objects, setting up data, or performing other actions that are required for the test to run correctly.

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4. Invoke the unit of code that you are testing, and capture the result.

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5. Use assertions to verify that the result of the code matches the expected result. An assertion is a statement that specifies a condition that must be true in order for the test to pass.

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6. Run the test, and check the results. If the test passes, then the code is working as expected. If the test fails, then there is an error in the code that needs to be fixed.

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7. Refactor the code, if necessary. If the test passes, you can then improve the design and structure of the code, without changing its behavior.

## And What About Integration Tests?

An integration test in Java is a type of test that verifies the integration and communication between different components or modules of a Java application. 

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For example, if you have a Java application that consists of a front-end user interface, a back-end server, and a database, an integration test would verify that all of these components are working together correctly and can exchange data as expected.

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To write an integration test in Java, you would typically create a separate test class and use testing tools like JUnit, RestAssured, or MockMvc to write and run your tests. In your test classes, you can build local Spring context and set up stubs to test any part of your application.

## What Tools Can I Use to Write Tests for Java Applications Today?

First, you need to remember that for test writing in the Java world the big player is Spring Framework. It already has many spring boot starters for testing. But if you want to use any simple solution, you can just take a look at very popular libraries for testing in Java:

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**Mockito:**

Mockito is a popular mocking framework for Java. It allows you to create mock objects and set up stub methods, which can then be used in your test cases to mimic the behavior of real objects and verify that your code is working as expected.

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With Mockito, you can write tests that are more robust and less susceptible to changes in the codebase, since the tests are isolated from the real objects and their dependencies. 

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This makes it easier to test individual units of code and can help you catch bugs and identify areas of your code that need further refinement.

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To use Mockito in your Java project, you will need to include the Mockito library in your classpath. Then, you can use the Mockito API to create mock objects and set up stub methods, as well as to verify that your code is behaving as expected. 

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For more detailed information on how to use Mockito, you can refer to the official documentation or check out some online tutorials.

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**JUnit:**

JUnit is a unit testing framework for the Java programming language. It is used to write and run repeatable tests for your Java code. With JUnit, you can test individual units of code and ensure that they are working correctly, without having to test the entire application.

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JUnit provides a set of annotations and assert methods that you can use to write your test cases. For example, you can use the `@Test` annotation to mark a method as a test method, and the `assertEquals` method to verify that the expected result matches the actual result. 

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JUnit also provides support for running tests in parallel and generating test reports.

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Using JUnit can help you catch and fix bugs in your code early in the development process, which can save you time and effort in the long run. It can also help you ensure that your code is working correctly and meets the requirements of your project. 

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To learn more about JUnit and how to use it in your Java project, you can refer to the official documentation or check out some online tutorials.


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