> ## Documentation Index
> Fetch the complete documentation index at: https://notes.kodekloud.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Unit Tests Basics

> This article covers unit testing practices, running tests with Maven, and measuring code coverage using JaCoCo.

Unit testing is a software development practice where individual units—such as functions, methods, or classes—are tested in isolation to ensure they behave as expected. By adopting unit tests early, teams can:

| Benefit                        | Description                                                           |
| ------------------------------ | --------------------------------------------------------------------- |
| Early Defect Detection         | Identify bugs at the development stage before they propagate.         |
| Faster Feedback Loop           | Run tests quickly and fix issues immediately.                         |
| Lower Maintenance Costs        | Catching issues early reduces expensive, late-stage fixes.            |
| Improved Code Quality & Design | Writing tests encourages cleaner, modular code and better API design. |

## Running Unit Tests with Maven

In a Maven-based project, execute all unit tests with:

```bash theme={null}
mvn test
```

Maven automatically scans `src/test/java` (and any additional test directories you’ve configured), runs tests, and fails the build if any test does not pass:

```bash theme={null}
[INFO] -------------------------------------------------------
[INFO]  T E S T S
[INFO] -------------------------------------------------------
[ERROR] Tests run: 3, Failures: 1, Errors: 0, Skipped: 0
[INFO] -------------------------------------------------------
[INFO] BUILD FAILURE
[INFO] -------------------------------------------------------
[INFO] Total time:  30.123 s
[INFO] Finished at: 2024-06-15T14:22:10+00:00
[INFO] -------------------------------------------------------
```

<Callout icon="lightbulb" color="#1CB2FE">
  By default, Maven looks for test classes matching `**/*Test.java` under `src/test/java`. You can customize this in the `<build><plugins>` section of your `pom.xml`.
</Callout>

<Callout icon="triangle-alert" color="#FF6B6B">
  A failing test will stop the Maven build. Ensure you fix or temporarily disable flaky tests to keep CI pipelines green.
</Callout>

## Measuring Code Coverage with JaCoCo

[JaCoCo](https://www.eclemma.org/jacoco/) is the de facto tool for generating Java code coverage reports. When integrated into Maven, it produces detailed HTML reports showing line and branch coverage.

### 1. Add the JaCoCo Plugin

Include the following snippet in your `pom.xml` under `<build><plugins>`:

```xml theme={null}
<plugin>
  <groupId>org.jacoco</groupId>
  <artifactId>jacoco-maven-plugin</artifactId>
  <version>0.8.10</version>
  <executions>
    <execution>
      <goals>
        <goal>prepare-agent</goal>
      </goals>
    </execution>
    <execution>
      <id>report</id>
      <phase>test</phase>
      <goals>
        <goal>report</goal>
      </goals>
    </execution>
  </executions>
</plugin>
```

<Callout icon="lightbulb" color="#1CB2FE">
  You can configure coverage thresholds to enforce minimum percentages. If thresholds are not met, the build will fail.
</Callout>

### 2. Generate the Report

Run your tests and generate the coverage report:

```bash theme={null}
mvn clean test
```

After completion, open:

```text theme={null}
target/site/jacoco/index.html
```

to view:

* **Overall Coverage:** Total percentage of covered code.
* **Per-Package/Class Breakdown:** Drill down into modules.
* **Covered vs. Uncovered Lines:** Visual indicators in source code.

| Report Section | Description                               |
| -------------- | ----------------------------------------- |
| Summary        | High-level percentages for lines/branches |
| Packages       | Coverage grouped by Java packages         |
| Classes        | Detailed per-class metrics                |
| Source Code    | Color-coded, line-by-line coverage view   |

## Links and References

* [JaCoCo Official Site](https://www.eclemma.org/jacoco/)
* [Maven Surefire Plugin](https://maven.apache.org/surefire/maven-surefire-plugin/)
* [JUnit 5 User Guide](https://junit.org/junit5/docs/current/user-guide/)

Thank you for reading!

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