Add basic DSL based on Gradle TestKit for KGP integration tests.

^KT-45744 In Progress

libraries/tools/kotlin-gradle-plugin-integration-tests/build.gradle.kts

@@ -39,6 +39,7 @@ dependencies {
     testImplementation(commonDep("org.jetbrains.intellij.deps", "trove4j"))
 
     testImplementation(gradleApi())
+    testImplementation(gradleTestKit())
     testImplementation("com.google.code.gson:gson:${rootProject.extra["versions.jar.gson"]}")
     testApiJUnit5(vintageEngine = true)
 

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

@@ -0,0 +1,21 @@
+/*
+ * Copyright 2010-2021 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.testbase
+
+import org.junit.jupiter.api.io.TempDir
+import java.nio.file.Path
+
+/**
+ * Base class for all Kotlin Gradle plugin integration tests.
+ */
+abstract class KGPBaseTest {
+
+    companion object {
+        @TempDir
+        @JvmStatic
+        lateinit var workingDir: Path
+    }
+}

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

@@ -0,0 +1,23 @@
+/*
+ * Copyright 2010-2021 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
+
+import org.intellij.lang.annotations.Language
+
+@Language("Groovy")
+internal val DEFAULT_GROOVY_SETTINGS_FILE =
+    """
+    pluginManagement {
+        repositories {
+            mavenLocal()
+            mavenCentral()
+        }
+
+        plugins {
+            id "org.jetbrains.kotlin.jvm" version "${'$'}kotlin_version"
+        }
+    }
+    """.trimIndent()

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

@@ -0,0 +1,116 @@
+/*
+ * Copyright 2010-2021 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.testbase
+
+import org.gradle.testkit.runner.BuildResult
+import org.gradle.testkit.runner.GradleRunner
+import org.jetbrains.kotlin.gradle.DEFAULT_GROOVY_SETTINGS_FILE
+import kotlin.test.assertTrue
+import java.nio.file.*
+import java.nio.file.Files.copy
+import java.nio.file.Files.createDirectories
+
+import java.nio.file.attribute.BasicFileAttributes
+
+/**
+ * Create new test project.
+ *
+ * @param [projectName] test project name in 'src/test/resources/testProject` directory.
+ */
+fun KGPBaseTest.project(
+    projectName: String,
+    test: TestProject.() -> Unit
+): TestProject {
+    val projectPath = setupProjectFromTestResources(projectName, KGPBaseTest.workingDir)
+    projectPath.addDefaultBuildFiles()
+
+    val gradleRunner = GradleRunner
+        .create()
+        .withProjectDir(projectPath.toFile())
+        .withTestKitDir(KGPBaseTest.workingDir.testKitDir.toFile())
+
+    val testProject = TestProject(gradleRunner, projectName)
+    testProject.test()
+    return testProject
+}
+
+/**
+ * Trigger test project build with given [buildArguments] and assert build is successful.
+ */
+fun TestProject.build(
+    vararg buildArguments: String,
+    assertions: BuildResult.() -> Unit = {}
+) {
+    println("<=== Test build: ${this.projectName} ===>")
+    val buildResult = gradleRunner
+        .withArguments(*buildArguments, "-Pkotlin_version=1.5.255-SNAPSHOT")
+        .build()
+    assertions(buildResult)
+}
+
+/**
+ * Trigger test project build with given [buildArguments] and assert build is failed.
+ */
+fun TestProject.buildAndFail(
+    vararg buildArguments: String,
+    assertions: BuildResult.() -> Unit = {}
+) {
+    println("<=== Test build: ${this.projectName} ===>")
+    val buildResult = gradleRunner
+        .withArguments(*buildArguments, "-Pkotlin_version=1.5.255-SNAPSHOT")
+        .buildAndFail()
+    assertions(buildResult)
+}
+
+class TestProject(
+    val gradleRunner: GradleRunner,
+    val projectName: String
+)
+
+private val Path.testKitDir get() = resolve("testKitDir")
+
+private fun setupProjectFromTestResources(
+    projectName: String,
+    tempDir: Path
+): Path {
+    val testProjectPath = Paths.get("src", "test", "resources", "testProject", projectName)
+    assertTrue("Test project exists") { Files.exists(testProjectPath) }
+    assertTrue("Test project path is a directory") { Files.isDirectory(testProjectPath) }
+
+    return tempDir
+        .resolve(projectName)
+        .also {
+            testProjectPath.copyRecursively(it)
+        }
+}
+
+private fun Path.addDefaultBuildFiles() {
+    if (Files.exists(resolve("build.gradle")) &&
+        !Files.exists(resolve("settings.gradle"))
+    ) {
+        resolve("settings.gradle").toFile().writeText(DEFAULT_GROOVY_SETTINGS_FILE)
+    }
+}
+
+private fun Path.copyRecursively(dest: Path) {
+    Files.walkFileTree(this, object : SimpleFileVisitor<Path>() {
+        override fun preVisitDirectory(
+            dir: Path,
+            attrs: BasicFileAttributes
+        ): FileVisitResult {
+            createDirectories(dest.resolve(relativize(dir)))
+            return FileVisitResult.CONTINUE
+        }
+
+        override fun visitFile(
+            file: Path,
+            attrs: BasicFileAttributes
+        ): FileVisitResult {
+            copy(file, dest.resolve(relativize(file)))
+            return FileVisitResult.CONTINUE
+        }
+    })
+}