diff --git a/libraries/stdlib/wasm/build.gradle.kts b/libraries/stdlib/wasm/build.gradle.kts
index bf5ce4f7cc2..3e317e084e2 100644
--- a/libraries/stdlib/wasm/build.gradle.kts
+++ b/libraries/stdlib/wasm/build.gradle.kts
@@ -53,10 +53,32 @@ val commonMainSources by task<Sync> {
     into("$buildDir/commonMainSources")
 }
 
+val commonTestSources by task<Sync> {
+    val sources = listOf(
+        "libraries/stdlib/test/",
+        "libraries/stdlib/common/test/"
+    )
+
+    sources.forEach { path ->
+        from("$rootDir/$path") {
+            into(path.dropLastWhile { it != '/' })
+        }
+    }
+
+    into("$buildDir/commonTestSources")
+}
+
 kotlin {
     wasm {
-        nodejs()
+        nodejs {
+            testTask {
+                useMocha {
+                    timeout = "10s"
+                }
+            }
+        }
     }
+
     sourceSets {
         val wasmMain by getting {
             kotlin.srcDirs("builtins", "internal", "runtime", "src", "stubs")
@@ -67,6 +89,20 @@ kotlin {
         val commonMain by getting {
             kotlin.srcDirs(files(commonMainSources.map { it.destinationDir }))
         }
+
+        val commonTest by getting {
+            dependencies {
+                api(project(":kotlin-test:kotlin-test-wasm"))
+            }
+            kotlin.srcDir(files(commonTestSources.map { it.destinationDir }))
+        }
+
+        val wasmTest by getting {
+            dependencies {
+                api(project(":kotlin-test:kotlin-test-wasm"))
+            }
+            kotlin.srcDir("$rootDir/libraries/stdlib/wasm/test/")
+        }
     }
 }
 
@@ -90,6 +126,15 @@ tasks.named("compileKotlinWasm") {
     dependsOn(builtInsSources)
 }
 
+val compileTestKotlinWasm by tasks.existing(KotlinCompile::class) {
+    val sources: FileCollection = kotlin.sourceSets["commonTest"].kotlin
+    doFirst {
+        // Note: common test sources are copied to the actual source directory by commonMainSources task,
+        // so can't do this at configuration time:
+        kotlinOptions.freeCompilerArgs += listOf("-Xcommon-sources=${sources.joinToString(",")}")
+    }
+}
+
 val runtimeElements by configurations.creating {}
 val apiElements by configurations.creating {}
 
diff --git a/libraries/stdlib/wasm/builtins/kotlin/Primitives.kt b/libraries/stdlib/wasm/builtins/kotlin/Primitives.kt
index 39ca9154f50..f43be80ef30 100644
--- a/libraries/stdlib/wasm/builtins/kotlin/Primitives.kt
+++ b/libraries/stdlib/wasm/builtins/kotlin/Primitives.kt
@@ -1493,6 +1493,18 @@ public class Float private constructor(public val value: Float) : Number(), Comp
          */
         @Suppress("DIVISION_BY_ZERO")
         public val NaN: Float = 0.0f / 0.0f
+
+        /**
+         * The number of bytes used to represent an instance of Float in a binary form.
+         */
+        @SinceKotlin("1.4")
+        public const val SIZE_BYTES: Int = 4
+
+        /**
+         * The number of bits used to represent an instance of Float in a binary form.
+         */
+        @SinceKotlin("1.4")
+        public const val SIZE_BITS: Int = 32
     }
 
     /**
@@ -1801,6 +1813,18 @@ public class Double private constructor(public val value: Double) : Number(), Co
          */
         @Suppress("DIVISION_BY_ZERO")
         public val NaN: Double = 0.0 / 0.0
+
+        /**
+         * The number of bytes used to represent an instance of Double in a binary form.
+         */
+        @SinceKotlin("1.4")
+        public const val SIZE_BYTES: Int = 8
+
+        /**
+         * The number of bits used to represent an instance of Double in a binary form.
+         */
+        @SinceKotlin("1.4")
+        public const val SIZE_BITS: Int = 64
     }
 
     /**
diff --git a/libraries/stdlib/wasm/test/collectionStubs.kt b/libraries/stdlib/wasm/test/collectionStubs.kt
new file mode 100644
index 00000000000..a0480104e41
--- /dev/null
+++ b/libraries/stdlib/wasm/test/collectionStubs.kt
@@ -0,0 +1,11 @@
+/*
+ * 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 test.collections.js
+
+public actual fun <V> stringMapOf(vararg pairs: Pair<String, V>): HashMap<String, V> = hashMapOf<String, V>(*pairs)
+public actual fun <V> linkedStringMapOf(vararg pairs: Pair<String, V>): LinkedHashMap<String, V> = linkedMapOf(*pairs)
+public actual fun stringSetOf(vararg elements: String): HashSet<String> = hashSetOf(*elements)
+public actual fun linkedStringSetOf(vararg elements: String): LinkedHashSet<String> = linkedSetOf(*elements)
diff --git a/libraries/stdlib/wasm/test/stringEncoding.kt b/libraries/stdlib/wasm/test/stringEncoding.kt
new file mode 100644
index 00000000000..ab5a16b37bd
--- /dev/null
+++ b/libraries/stdlib/wasm/test/stringEncoding.kt
@@ -0,0 +1,11 @@
+/*
+ * 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 test.text
+
+// TODO: Fix this once we implement kotlin.text
+internal actual val surrogateCodePointDecoding: String = "�"
+
+internal actual val surrogateCharEncoding: ByteArray = byteArrayOf(0x3F)
diff --git a/libraries/stdlib/wasm/test/testUtils.kt b/libraries/stdlib/wasm/test/testUtils.kt
new file mode 100644
index 00000000000..36e5e241014
--- /dev/null
+++ b/libraries/stdlib/wasm/test/testUtils.kt
@@ -0,0 +1,33 @@
+/*
+ * 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 test
+
+import kotlin.test.*
+
+public actual fun assertTypeEquals(expected: Any?, actual: Any?) {
+    TODO("Implement class references")
+    //assertEquals(expected?.let { it::class.js }, actual?.let { it::class.js })
+}
+
+@Suppress("NOTHING_TO_INLINE")
+internal actual inline fun String.removeLeadingPlusOnJava6(): String = this
+
+internal actual inline fun testOnNonJvm6And7(f: () -> Unit) {
+    f()
+}
+
+
+public actual fun testOnJvm(action: () -> Unit) { }
+public actual fun testOnJs(action: () -> Unit) { }
+
+// TODO: See KT-24975
+public actual val isFloat32RangeEnforced: Boolean = false
+
+// TODO: We need to implement this on wasm
+actual val supportsSuppressedExceptions: Boolean get() = false
+
+// TODO: implement named group reference in replacement expression
+public actual val supportsNamedCapturingGroup: Boolean get() = false