Multi-project test dependencies with gradle

This is now supported as a first class feature in Gradle. Modules with java or java-library plugins can also include a java-test-fixtures plugin which exposes helper classes and resources to be consumed with testFixtures helper. Benefit of this approach against artifacts and classifiers are:

• proper dependency management (implementation/api)
• nice separation from test code (separate source set)
• no need to filter out test classes to expose only utilities
• maintained by Gradle

Example

:modul:one

modul/one/build.gradle

plugins {
  id "java-library" // or "java"
  id "java-test-fixtures"
}

modul/one/src/testFixtures/java/com/example/Helper.java

package com.example;
public class Helper {}

:modul:other

modul/other/build.gradle

plugins {
  id "java" // or "java-library"
}
dependencies {
  testImplementation(testFixtures(project(":modul:one")))
}

modul/other/src/test/java/com/example/other/SomeTest.java

package com.example.other;
import com.example.Helper;
public class SomeTest {
  @Test void f() {
    new Helper(); // used from :modul:one's testFixtures
  }
}

Further reading

For more info, see the documentation:
https://docs.gradle.org/current/userguide/java_testing.html#sec:java_test_fixtures

It was added in 5.6:
https://docs.gradle.org/5.6/release-notes.html#test-fixtures-for-java-projects

Deprecated - For Gradle 5.6 and above use this answer.

In Project B, you just need to add a testCompile dependency:

dependencies {
  ...
  testCompile project(':A').sourceSets.test.output
}

Tested with Gradle 1.7.