Mastering Mockito: Simplify Java Unit Tests with Powerful Mocking

What is Mockito?

Mockito is a powerful Java mocking framework that allows developers to create and configure mock objects, simplifying testing of classes with external dependencies by defining input‑output behavior without implementing the actual method logic.

When to Use Mockito

It is suitable for unit testing methods that depend on external services such as REST APIs, client‑server calls, or database queries, where constructing real dependencies would be cumbersome.

How to Use Mockito

Add Dependency Maven dependency:

<dependency>
  <groupId>org.mockito</groupId>
  <artifactId>mockito-core</artifactId>
  <version>1.10.19</version>
  <scope>test</scope>
</dependency>

Create Mock Objects In Scala you can only mock companion objects or classes, not plain objects. Use Mockito.mock(classOf[...]) to create a mock.

class VpcClient {
  def getRouteTable(projectId: String, token: String, url: String): Seq[RouteTable] = {
    val header = Map(RequestAttributes.X_AUTH_TOKEN -> token,
      "Content-Type" -> MediaType.APPLICATION_JSON)
    val response = restClient.get(url, header)
  }
}
object VpcClient {
  private lazy val _instance: VpcClient = new VpcClient(conf)
  private var mockClient: VpcClient = _
  def getInstance(): VpcClient = {
    if (RuntimeEnvironment.isTesting && null != mockClient) {
      return mockClient
    }
    _instance
  }
  def setMockClient(vpcClient: VpcClient): Unit = {
    mockClient = vpcClient
  }
}

Configure Mock Behavior Use Mockito.doReturn(...).when(mock).method(args) to specify the return value for a given input.

Mockito.doReturn(routeTableInfo)
  .when(vpcClient).getRouteTable(projectId, token, url)

Summary

The article outlines Mockito’s use cases, demonstrates how to add the Maven dependency, create mock objects in Scala, and configure their behavior, noting minor differences from Java usage.

References

Official site: http://mockito.org

API documentation: http://docs.mockito.googlecode.com/hg/org/mockito/Mockito.html

Source code: https://github.com/mockito/mockito