Building a Gradle project

Tips for successfully building a Gradle project - an essential prerequisite for using Cover CLI.

Compiling the project

If your project uses the Gradle build system, cd into the directory containing the build script (build.gradle or build.gradle.kts), this is typically located at the root of your repository.

To compile the project, if a gradlew (or gradlew.bat on Windows) file is present, run the ./gradlew build command, otherwise run gradle build.

It is generally preferable to execute Gradle commands using ./gradlew (or gradlew.bat on Windows) rather than gradle if these Gradle wrapper scripts are present in your project.

In either case, if successful, you should see a BUILD SUCCESSFUL message towards the end of the output from Gradle:

7 actionable tasks: 2 executed, 5 up-to-date

In order to run Diffblue Cover CLI it is essential that your Gradle project builds successfully. If it finds a Gradle project, Cover will call Gradle to determine your project settings. If your Gradle project fails then Cover will exit with an error message (and reason):

ERROR An error was encountered while building the Gradle project at ...

If there is a Gradle wrapper for your project (gradlew, gradlew.bat), Cover will use the wrapper's declared version in preference to your system's installed Gradle version.

Gradle and user-specified system properties

The -D or --define option allows the user to pass additional system properties to dcover for test creation and execution.

Any created tests may depend upon these user-specified system properties and may not execute successfully without them.

Unfortunately by default Gradle does not forward command line system properties to test execution. Therefore out-of-the-box dcover may fail to validate your tests.

You can overcome this issue with additional configuration. If you have supplied these system properties to dcover:

dcover create -Dproperty1=value1 -Dproperty2=value2

Then you must also supply those same system properties to Gradle test execution before running dcover create.

Specify your system properties in the test task:

test {
  systemProperty 'property1', 'value1'
  systemProperty 'property2', 'value2'

Keeping these properties in sync will ensure that test validation will succeed and that your created tests can be executed successfully from Gradle.

Gradle Troubleshooting

JUnit Jupiter Platform Launcher jar

When using JUnit Jupiter, dcover relies upon the JUnit Platform Launcher jar to verify created tests. Without this jar dcover will not be able to verify that created tests execute successfully in your build environment. You may see this warning message if the launcher jar is not available from your test configuration:

13:11:32.487 INFO Checking test environment...
13:11:39.515 ERROR E011: Problems in the local build environment have been detected that will prevent Diffblue Cover from validating the generated tests.

To prevent this issue you must configure your build script to supply the corresponding junit-platform-launcher for your JUnit engine at test runtime:

dependencies {

In the example above 1.7.1 is the correct version of the platform launcher for the 5.7.1 version of the engine. See the JUnit user guide for further details about this.

Checkstyle Plugin

If dcover cannot verify the tests it creates due to an incompatibility with the stylecheck used in your environment, you will receive an error message.

If your project uses the Gradle Checkstyle plugin (, amend the build script to exclude Diffblue tests, as shown in the example below:

tasks.withType(Checkstyle) {
    exclude '**/*DiffblueTest**'

Debugging Information

Class files should be compiled with debug information included for Diffblue Cover to write the best tests possible. If you have switched off debug information, please switch it back on again:

tasks.withType(JavaCompile) {
  configure(options) {
    options.debug = true

The underlying javac Java compiler can use a -g option to generate all debugging information, if you're using custom compiler arguments then please ensure the -g option and not -g:none are present.

For Gradle documentation, see CompileOptions.

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