Add tests from the reverted commit

To ensure deterministic build outputs.

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

@@ -0,0 +1,93 @@
+/*
+ * Copyright 2010-2020 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.jetbrains.kotlin.gradle.util.allJavaFiles
+import org.junit.Test
+import java.io.File
+import kotlin.test.assertEquals
+
+/** Tests that the outputs of a build are deterministic. */
+class DeterministicBuildIT : BaseGradleIT() {
+
+    @Test
+    fun `test KaptGenerateStubsTask - KT-40882`() = with(
+        Project("simple", directoryPrefix = "kapt2")
+    ) {
+        setupWorkingDir()
+        projectDir
+            .resolve("src/main/java/Foo.kt")
+            .writeText(
+                """
+                class Foo : Bar {
+                    // The fields and methods are ordered such that any sorting by KGP will be detected.
+                    val fooField1 = 1
+                    val fooField3 = 3
+                    val fooField2 = 2
+                    fun fooMethod1() {}
+                    fun fooMethod3() {}
+                    fun fooMethod2() {}
+                }
+                """.trimIndent()
+            )
+        projectDir
+            .resolve("src/main/java/Bar.kt")
+            .writeText(
+                """
+                interface Bar {
+                    val barField1 = 1
+                    val barField3 = 3
+                    val barField2 = 2
+                    fun barMethod1() {}
+                    fun barMethod3() {}
+                    fun barMethod2() {}
+                }
+                """.trimIndent()
+            )
+
+        val buildAndSnapshotStubFiles: () -> Map<File, String> = {
+            lateinit var stubFiles: Map<File, String>
+            build(":kaptGenerateStubsKotlin") {
+                assertSuccessful()
+                assertTasksExecuted(":kaptGenerateStubsKotlin")
+                stubFiles = fileInWorkingDir("build/tmp/kapt3/stubs").allJavaFiles().map {
+                    it to it.readText()
+                }.toMap()
+            }
+            stubFiles
+        }
+
+        // Run the first build
+        val stubFilesAfterFirstBuild = buildAndSnapshotStubFiles()
+
+        // Make a change
+        projectDir.resolve("src/main/java/Foo.kt").also {
+            it.writeText(
+                """
+                class Foo : Bar {
+                    val fooField1 = 1
+                    val fooField3 = 3
+                    val fooField2 = 2
+                    fun fooMethod1() { println("Method body changed!") }
+                    fun fooMethod3() {}
+                    fun fooMethod2() {}
+                }
+                """.trimIndent()
+            )
+        }
+
+        // Run the second build
+        val stubFilesAfterSecondBuild = buildAndSnapshotStubFiles()
+
+        // Check that the build outputs are deterministic
+        assertEquals(stubFilesAfterFirstBuild.size, stubFilesAfterSecondBuild.size)
+        for (file in stubFilesAfterFirstBuild.keys) {
+            val fileContentsAfterFirstBuild = stubFilesAfterFirstBuild[file]
+            val fileContentsAfterSecondBuild = stubFilesAfterSecondBuild[file]
+            assertEquals(fileContentsAfterFirstBuild, fileContentsAfterSecondBuild)
+        }
+    }
+}