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A few points first...

Cover components

Cover is provided as an IDE plugin tool so you can write tests with one click in the IntelliJ IDE (Cover Plugin), a CLI application to write tests for your entire project (Cover CLI), and a CI integration to automatically write tests within your CI workflow (Cover Pipeline).

Perfect partners

Cover Plugin, Cover CLI, and Cover Pipeline are not mutually exclusive, in fact they make perfect partners. Use Cover Plugin within the IntelliJ IDE to write and check unit tests for your application during development, and also use Cover CLI directly from the IntelliJ Terminal/Console or your OS command line to access the wider and deeper functionality provided by Cover CLI - finally, use Cover Pipeline within your CI tool to automate the whole process and provide consistency across your organisation.

The free trial

This topic focuses on Cover Plugin and Cover CLI, and will take you through the key steps to download, install, and license both tools, as well as covering a few basics and getting some tests written using each tool. Cover Pipeline for GitLab is also available as a free trial version, see Cover Pipeline for GitLab for details - for all other CI integrations please contact Diffblue.

1. Sign up

If you haven't already done so, sign up for the free trial - see https://www.diffblue.com/try-cover.

After successful sign-up, you'll receive a welcome email with general information and a license key for Cover Plugin and Cover CLI.

2. Install Cover Plugin for IntelliJ

  1. In the IntelliJ IDE, open the Plugins menu - either File > Settings > Plugins (Windows/Linux) or IntelliJ IDEA > Preferences > Plugins (macOS).

  2. Select the Marketplace tab, search for Diffblue, and click Install. Your plugin will now be downloaded and installed.

  3. When prompted, click Restart IDE to complete the install.

3. Install Cover CLI

  1. Download the Diffblue Cover CLI .exe installer or .zip file from: - The Diffblue website - Free Trial version. - The link sent to you via your Diffblue Cover welcome email. - Your organization's internal file/app store.\

  2. If you use the installer, run the .exe installer and follow the on-screen prompts - during installation you can select where to install Diffblue Cover.

  3. If you use the archive file, extract the .zip file to an appropriate installation folder. Add the install folder path to your the PATH environment variable or create a new %DCOVER% environment variable and add that to PATH.

  4. When your done, restart your PC. Once complete, open Windows PowerShell and enter dcover version to check the install and PATH configuration - if all is OK, Cover will display the current version.

4. Apply licenses

Once IntelliJ has restarted (after install), you'll be prompted for your license key (provided in your welcome email or by your organization) to activate the plugin. Diffblue Cover requires a remote license check with the Diffblue licensing server each time it's used. For help troubleshooting license keys, network connections, and proxy server settings, see Licensing. Note that:

  • Applying a license provides access to the Teams and Enterprise Editions of Diffblue Cover.

  • Cover Plugin Community Edition is free to use but does require product verification to activate your perpetual license.

  • Offline license activation is available with the Diffblue Cover Enterprise Edition only. This can only be done through the CLI.

  • See Cover Editions and Licensing for more details.

5. Try it out

Four steps to automatically write tests - clone an example project, compile the project and check your environment, learn a few basics, and then one click or one command to write tests.

Step 1 - Clone the example project Spring PetClinic

We're going to make use of an example project (Spring PetClinic) to show the Diffblue Cover Plugin for IntelliJ at work. First, we'll clone the project from the Git repo:

  1. Open a command line and navigate to where you want to clone this project.

  2. Run the following command:

git clone https://github.com/diffblue/demo-spring-petclinic

Step 2 - Compile the project and check your environment

Before we write any tests, we need to compile the PetClinic project. Diffblue Cover works by analyzing the bytecode of any project used with Cover. You can do this from the Maven plugin in IntelliJ (click the Maven tab, open petclinic > Lifecycle, and double-click package) or open a command line, navigate to the directory containing the PetClinic project, and run the Maven package command:

cd demo-spring-petclinic
./mvnw package

Basic prerequisites:

  • Java 8, 11, 17, or 21 compatible source code, or Kotlin source code.

  • Maven 3.2.5+ or Gradle 4.9+ build tools.

  • Any project (for use with Diffblue Cover) must compile and run with no failing unit tests. JUnit and TestNG testing frameworks are supported.

More details:

Diffblue Cover requires that the system environment (hardware, operating system, network connectivity, Java installation) as well as the project environment (build tooling, dependencies, presence of artifacts, existing unit tests) meet the minimum requirements as detailed in Specs & Reqs. Cover will perform an environment check before analysis begins to ensure that the requirements are met - if there are any issues, these will be reported via the Diffblue Cover panel in IntelliJ using E(Environment) Output Codes.

Check your environment:

Cover CLI also provides a command line option to run these checks, without writing any tests, useful when you just want to check-out your environment without doing anything else. To run a preflight environment check, open a command line, navigate to the directory containing the PetClinic project, and run the preflight checks:

cd demo-spring-petclinic
dcover create --preflight

Step 3 - A few basics

Before we start using Diffblue Cover to write tests, it's worth covering a few basics first.

We won't cover the whole UI here, but here are a few useful gutter icons to get you started:

IconDescription

Write tests - click this icon to write tests for this method or class.

Not testable - this method or class can't be tested. Click the icon to find out why.

Private method - this method can't be tested as it's private, although it may be tested indirectly via a public method. If you'd like Cover to write unit tests for this method, you can either make the method public or package protected.

Test maintenance - displayed next to test classes and methods in project test files. Click the icon to update or delete tests for the method or class.

Delete test - displayed next to your test methods in project test files. Click the icon to delete a test method.

Step 4 - Automatically write tests for the example project

In this step we're going to use Diffblue Cover to automatically write tests for two classes and then for the entire PetClinic project. We'll make use of Cover Plugin for IntelliJ and run Cover CLI commands from a command line. You can also use Cover CLI straight from the IntelliJ terminal - handy when you’re using both tools in partnership

Note that the examples here use DiffblueTest as the default class name suffix and diffbluetest as the default method name prefix, just to highlight the tests created by Diffblue Cover.

  • To change your suffix and prefix in IntelliJ, go to Diffblue > Change Settings > Test Naming > Class Template/Method Template.

  • To change your suffix and prefix in Cover CLI, use the --class-name-template and --method-name-template command arguments - see Cover CLI Commands & Arguments for details.


First we'll use Cover Plugin for IntelliJ:

  1. In IntelliJ, open the PetClinic project and navigate to a class - for example, OwnerController.

  2. Click the links in the Diffblue Cover panel to see the tests produced. And that's it, simple - 1 click, 9 methods analyzed, 7 tests written, around 340 lines of code, and all in around 65 seconds - computationally perfect, human readable. You'll find these tests in the test folder for the project.

package org.springframework.samples.petclinic.owner;

import ...

@ContextConfiguration(classes = {OwnerController.class})
@ExtendWith(SpringExtension.class)
class OwnerControllerDiffblueTest {
	@Autowired
	private OwnerController ownerController;

	@MockBean
	private OwnerRepository ownerRepository;

	/**
	 * Method under test: {@link OwnerController#initCreationForm(Map)}
	 */
	@Test
	void diffbluetestInitCreationForm() throws Exception {
		MockHttpServletRequestBuilder requestBuilder = MockMvcRequestBuilders.get("/owners/new");
		MockMvcBuilders.standaloneSetup(ownerController)
			.build()
			.perform(requestBuilder)
			.andExpect(MockMvcResultMatchers.status().isOk())
			.andExpect(MockMvcResultMatchers.model().size(1))
			.andExpect(MockMvcResultMatchers.model().attributeExists("owner"))
			.andExpect(MockMvcResultMatchers.view().name("owners/createOrUpdateOwnerForm"))
			.andExpect(MockMvcResultMatchers.forwardedUrl("owners/createOrUpdateOwnerForm"));
	}

....

Now we'll move on to using Cover CLI.

  1. Open a command line or open the IntelliJ terminal, and navigate to the demo-spring-petclinic folder.

  2. Enter the following command to write tests for the PetController class:

dcover create org.springframework.samples.petclinic.owner.PetController
  1. Cover CLI will now write the tests for the class - 1 command line, 10 methods analyzed, 9 tests written, around 214 lines of code created, and again, all in around 65 seconds - computationally perfect, human readable. You'll find these tests in the test folder for the project.

package org.springframework.samples.petclinic.owner;

import ...

@ContextConfiguration(classes = {PetController.class})
@ExtendWith(SpringExtension.class)
class PetControllerDiffblueTest {
	@MockBean
	private OwnerRepository ownerRepository;

	@Autowired
	private PetController petController;

	/**
	 * Method under test: {@link PetController#populatePetTypes()}
	 */
	@Test
	void diffbluetestPopulatePetTypes() {
		ArrayList<PetType> petTypeList = new ArrayList<>();
		when(ownerRepository.findPetTypes()).thenReturn(petTypeList);
		Collection<PetType> actualPopulatePetTypesResult = petController.populatePetTypes();
		assertSame(petTypeList, actualPopulatePetTypesResult);
		assertTrue(actualPopulatePetTypesResult.isEmpty());
		verify(ownerRepository).findPetTypes();
	}
....
  1. Once you're happy with this first set of tests, create the full test suite for the entire PetClinic project - enter dcover create. That's it, two "words" and you're done. Of course this one takes a little longer to complete (around five minutes) as it creates tests across the entire PetClinic project, analyzing 97 methods and creating 77 tests (exact count may vary slightly).

More...

What does Diffblue Cover do?

  • Diffblue Cover first ensures that your code is compiled and examines each method that Cover will create tests for, including any dependent methods.

  • Cover then creates initial test candidates and uses reinforcement learning to evaluate and adjust the test candidate for each method. This process is repeated until the set of tests that optimize coverage are selected and committed to your code base.

Next steps

Now you're up and running with Diffblue Cover:

  • Have a scan through the Test examples topic which provides some additional source code examples along with an explanation of the tests created by Diffblue Cover.

  • Create some tests for your own project - as long as you have a project that compiles and your environment meets the Cover prerequisites, you're literally a click away from AI written tests, created in seconds instead of hours.

  • See Cover Plugin and Cover CLI to familiarize yourself with the full set of features and functions.

  • Cover Pipeline for GitLab is also available as a free trial version, see Cover Pipeline for GitLab for details - for all other CI integrations please contact Diffblue.

If you're only planning to use Cover Plugin Community Edition (free), you may just want to jump straight to the topic.

Notes

Demo code, statistics, and timings used throughout Diffblue docs and eLearning videos are based on in-house demonstrations. These may differ slightly from those experienced within a live production environment.

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