diff --git a/libraries/stdlib/build.gradle.kts b/libraries/stdlib/build.gradle.kts
index 3cebe520b59..cdf4b20658a 100644
--- a/libraries/stdlib/build.gradle.kts
+++ b/libraries/stdlib/build.gradle.kts
@@ -41,6 +41,7 @@ val builtinsRuntimeSrcDir = "${buildDir}/src/builtin-sources-for-runtime"
 
 val jsCommonDir = "${projectDir}/../js"
 val jsCommonSrcDir = "${jsCommonDir}/src"
+val jsCommonTestSrcDir = "${jsCommonDir}/test"
 val jsV1Dir = "${projectDir}/../js-v1"
 val jsSrcDir = "$jsV1Dir/src"
 val jsSrcJsDir = "${jsSrcDir}/js"
@@ -48,6 +49,7 @@ val jsSrcJsDir = "${jsSrcDir}/js"
 // for js-ir
 val jsIrDir = "${projectDir}/../js-ir"
 val jsIrMainSources = "${buildDir}/src/jsMainSources"
+val jsIrTestSources = "${buildDir}/src/jsTestSources"
 lateinit var jsIrTarget: KotlinJsTargetDsl
 
 kotlin {
@@ -76,12 +78,30 @@ kotlin {
                     )
                 }
             }
+            val test by getting {
+                kotlinOptions {
+                    // This is needed for JavaTypeTest; typeOf for non-reified type parameters doesn't work otherwise, for implementation reasons.
+                    freeCompilerArgs -= "-Xno-optimized-callable-references"
+                }
+            }
+            val longRunningTest by creating {
+                defaultSourceSet {
+                    dependencies {
+                        implementation(main.output.allOutputs)
+                    }
+                }
+            }
         }
     }
     js(LEGACY) {
         browser {
         }
         nodejs {
+            testTask {
+                useMocha {
+                    timeout = "10s"
+                }
+            }
         }
         compilations {
             all {
@@ -108,9 +128,15 @@ kotlin {
                     sourceMap = true
                 }
             }
+            val test by getting; test.apply {
+                kotlinOptions {
+                    moduleKind = "umd"
+                }
+            }
         }
     }
     jsIrTarget = js("jsIr", IR) {
+        browser {}
         nodejs {
             testTask {
                 useMocha {
@@ -145,6 +171,16 @@ kotlin {
                 srcDir("../unsigned/src")
             }
         }
+        commonTest {
+            dependencies {
+//                compileOnly(project(":kotlin-test:kotlin-test-common"))
+//                compileOnly(project(":kotlin-test:kotlin-test-annotations-common"))
+            }
+            kotlin.apply {
+                srcDir("../common/test")
+                srcDir("../test")
+            }
+        }
         val jvmMain by getting {
             project.configurations.getByName("jvmMainCompileOnly").extendsFrom(configurationBuiltins)
             dependencies {
@@ -159,6 +195,20 @@ kotlin {
             project.sourceSets["main"].java.srcDirs(*jvmSrcDirs)
         }
 
+        val jvmTest by getting {
+            dependencies {
+                api(project(":kotlin-test:kotlin-test-junit"))
+            }
+            kotlin.srcDir("../jvm/test")
+        }
+
+        val jvmLongRunningTest by getting {
+            dependencies {
+                api(project(":kotlin-test:kotlin-test-junit"))
+            }
+            kotlin.srcDir("../jvm/testLongRunning")
+        }
+
         val jsRuntime by getting {
             kotlin.apply {
                 srcDir(builtinsRuntimeSrcDir)
@@ -216,6 +266,15 @@ kotlin {
                 dependsOn(prepareBuiltinsSources)
             }
         }
+        val jsTest by getting {
+            dependencies {
+                api(project(":kotlin-test:kotlin-test-js-v1"))
+            }
+            kotlin.apply {
+                srcDir(jsCommonTestSrcDir)
+                srcDir("$jsV1Dir/test")
+            }
+        }
 
         val jsIrMain by getting {
             kotlin.apply {
@@ -278,6 +337,19 @@ kotlin {
                 dependsOn(prepareJsIrMainSources)
             }
         }
+        val jsIrTest by getting {
+            kotlin.srcDir(jsIrTestSources)
+            dependencies {
+                api(project(":kotlin-test:kotlin-test-js-ir"))
+            }
+            val prepareJsIrTestSources by tasks.registering(Sync::class) {
+                from(jsCommonTestSrcDir)
+                into(jsIrTestSources)
+            }
+            jsIrTarget.compilations["test"].compileKotlinTaskProvider.configure {
+                dependsOn(prepareJsIrTestSources)
+            }
+        }
 
         all {
             languageSettings {
@@ -287,6 +359,10 @@ kotlin {
                     optIn("kotlin.ExperimentalMultiplatform")
                     optIn("kotlin.contracts.ExperimentalContracts")
                 }
+                if (this@all.name.endsWith("Test")) {
+                    optIn("kotlin.ExperimentalUnsignedTypes")
+                    optIn("kotlin.ExperimentalStdlibApi")
+                }
             }
         }
     }
@@ -426,6 +502,17 @@ tasks {
             Files.copy(jsResultingJarFile.get().asFile.toPath(), archiveFile.get().asFile.toPath(), StandardCopyOption.REPLACE_EXISTING)
         }
     }
+
+
+    val jvmLongRunningTest by registering(Test::class) {
+        val compilation = kotlin.jvm().compilations["longRunningTest"]
+        classpath = compilation.compileDependencyFiles + compilation.runtimeDependencyFiles + compilation.output.allOutputs
+        testClassesDirs = compilation.output.classesDirs
+    }
+
+    if (project.hasProperty("kotlin.stdlib.test.long.running")) {
+        check.configure { dependsOn(jvmLongRunningTest) }
+    }
 }
 
 configureDefaultPublishing()
\ No newline at end of file