[Gradle] Add integration tests for KMP empty and non-test source sets

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/mpp/MppEmptyTestSourceSetsIT.kt

@@ -0,0 +1,124 @@
+/*
+ * Copyright 2010-2026 JetBrains s.r.o. and Kotlin Programming Language contributors.
+ * Use of this source code is governed by the Apache 2.0 license that can be found in the license/LICENSE.txt file.
+ */
+
+package org.jetbrains.kotlin.gradle.mpp
+
+import org.gradle.util.GradleVersion
+import org.jetbrains.kotlin.gradle.testbase.*
+import org.junit.jupiter.api.DisplayName
+
+@MppGradlePluginTests
+@DisplayName("Tests for empty MPP test source sets")
+class MppEmptyTestSourceSetsIT : KGPBaseTest() {
+
+    @DisplayName("No test sources in commonTest or jvmTest")
+    @GradleTest
+    fun testNoTestSources(gradleVersion: GradleVersion) {
+        project("base-kotlin-multiplatform-library", gradleVersion) {
+            buildScriptInjection {
+                kotlinMultiplatform.jvm()
+            }
+            kotlinSourcesDir("commonMain").source("CommonMain.kt") {
+                """
+                package org.example.project
+
+                fun commonFun(): String = "common"
+                """.trimIndent()
+            }
+
+            build(":jvmTest") {
+                assertTasksNoSource(":compileTestKotlinJvm", ":jvmTest")
+                assertNoTestResultsProduced("jvmTest")
+            }
+        }
+    }
+
+    // In Gradle 9.0+, executing a test task fails by default when test compilation outputs exist but 0 tests are discovered.
+    // Older Gradle versions succeeded silently.
+    @DisplayName("Sources in jvmTest without test cases fail on Gradle 9.0+")
+    @GradleTestVersions(minVersion = TestVersions.Gradle.G_9_0)
+    @GradleTest
+    fun testSourcesWithoutTests(gradleVersion: GradleVersion) {
+        project("base-kotlin-multiplatform-library", gradleVersion) {
+            buildScriptInjection {
+                kotlinMultiplatform.jvm()
+            }
+            kotlinSourcesDir("jvmTest").source("NotATest.kt") {
+                """
+                package org.example.project
+
+                class NotATest {
+                    fun helper(): String = "helper"
+                }
+                """.trimIndent()
+            }
+
+            buildAndFail(":jvmTest") {
+                assertTasksExecuted(":compileTestKotlinJvm")
+                assertTasksFailed(":jvmTest")
+                assertNoTestResultsProduced("jvmTest")
+            }
+        }
+    }
+
+    @DisplayName("Common test discovery and inheritance in jvmTest")
+    @GradleTest
+    fun testCommonTestDiscoveryAndInheritance(gradleVersion: GradleVersion) {
+        project("base-kotlin-multiplatform-library", gradleVersion) {
+            buildScriptInjection {
+                kotlinMultiplatform.jvm()
+                kotlinMultiplatform.sourceSets.getByName("commonTest").dependencies {
+                    implementation(kotlin("test"))
+                }
+            }
+            kotlinSourcesDir("commonTest").source("CommonSampleTest.kt") {
+                """
+                package org.example.project
+
+                import kotlin.test.Test
+                import kotlin.test.assertTrue
+
+                open class CommonSampleTest {
+                    @Test
+                    fun testInCommon() {
+                        assertTrue(true)
+                    }
+                }
+                """.trimIndent()
+            }
+
+            build(":jvmTest") {
+                assertTasksExecuted(":compileTestKotlinJvm", ":jvmTest")
+                assertExecutedTestCases("jvmTest", "org.example.project.CommonSampleTest#testInCommon")
+            }
+
+            kotlinSourcesDir("jvmTest").source("JvmSampleTest.kt") {
+                """
+                package org.example.project
+
+                import kotlin.test.Test
+                import kotlin.test.assertTrue
+
+                class JvmSampleTest : CommonSampleTest() {
+                    @Test
+                    fun testInJvm() {
+                        assertTrue(true)
+                    }
+                }
+                """.trimIndent()
+            }
+
+            build(":jvmTest") {
+                assertTasksExecuted(":compileTestKotlinJvm", ":jvmTest")
+                assertExecutedTestCases(
+                    "jvmTest",
+                    "org.example.project.CommonSampleTest#testInCommon",
+                    "org.example.project.JvmSampleTest#testInCommon",
+                    "org.example.project.JvmSampleTest#testInJvm",
+                )
+            }
+        }
+    }
+}

libraries/tools/kotlin-gradle-plugin-integration-tests/src/test/kotlin/org/jetbrains/kotlin/gradle/testbase/testAssertions.kt

@@ -20,6 +20,7 @@ import kotlin.io.path.absolutePathString
 import kotlin.io.path.name
 import kotlin.io.path.readText
 import kotlin.test.assertEquals
+import kotlin.test.assertTrue
 
 /**
  * @param stripBrowserVersionInfoFromTestCaseNames Some test executor implementations include browser version info in test case names,
@@ -63,6 +64,20 @@ fun GradleProject.assertTestResults(
     assertEquals(expectedTestResults, actualTestResults)
 }
 
+fun GradleProject.assertNoTestResultsProduced(
+    taskName: String,
+    subprojectName: String? = null,
+) {
+    val testResultsDir = testResultsAndReportsDirs(taskName, subprojectName).first
+    if (Files.exists(testResultsDir)) {
+        val xmlFiles = testResultsDir.allFilesWithExtension("xml")
+        assertTrue(
+            xmlFiles.isEmpty(),
+            "Expected no test result XML files in '$testResultsDir', but found: ${xmlFiles.joinToString()}"
+        )
+    }
+}
+
 internal fun readValidateAndCleanupTestResults(
     testReportDirs: List<Path>,
     projectPath: Path,