Refactor helper function to run/not run block of common code on specific platform

Use it in StringBuilder tests

libraries/stdlib/common/test/testUtils.kt

@@ -7,9 +7,6 @@ package test
 
 public expect fun assertTypeEquals(expected: Any?, actual: Any?)
 
-public expect fun testOnJvm(action: () -> Unit)
-public expect fun testOnJs(action: () -> Unit)
-
 public expect val isFloat32RangeEnforced: Boolean
 
 public expect val supportsNamedCapturingGroup: Boolean

libraries/stdlib/js/test/core/testUtils.kt

@@ -12,8 +12,7 @@ public actual fun assertTypeEquals(expected: Any?, actual: Any?) {
 }
 
 
-public actual fun testOnJvm(action: () -> Unit) { }
-public actual fun testOnJs(action: () -> Unit) = action()
+public actual val TestPlatform.Companion.current: TestPlatform get() = TestPlatform.Js
 
 // TODO: should be true at least in JS IR after implementing KT-24975
 public actual val isFloat32RangeEnforced: Boolean = false

libraries/stdlib/jvm/test/testUtilsJVM.kt

@@ -12,8 +12,7 @@ public actual fun assertTypeEquals(expected: Any?, actual: Any?) {
     assertEquals(expected?.javaClass, actual?.javaClass)
 }
 
-public actual fun testOnJvm(action: () -> Unit) = action()
-public actual fun testOnJs(action: () -> Unit) {}
+public actual val TestPlatform.Companion.current: TestPlatform get() = TestPlatform.Jvm
 
 @Suppress("HasPlatformType", "UNCHECKED_CAST")
 public fun <T> platformNull() = Collections.singletonList(null as T).first()

libraries/stdlib/test/testUtils.kt

@@ -10,6 +10,23 @@ import kotlin.test.assertEquals
 import kotlin.test.assertTrue
 import kotlin.test.fail
 
+public enum class TestPlatform {
+    Jvm,
+    Js,
+    Native,
+    Wasm;
+    companion object
+}
+
+public expect val TestPlatform.Companion.current: TestPlatform
+
+public fun testOn(platformPredicate: (TestPlatform) -> Boolean, action: () -> Unit) {
+    if (platformPredicate(TestPlatform.current)) action()
+}
+public fun testOnlyOn(platform: TestPlatform, action: () -> Unit) = testOn({ it == platform }, action)
+public fun testExceptOn(platform: TestPlatform, action: () -> Unit) = testOn({ it != platform}, action)
+
+
 // just a static type check
 @Suppress("INVISIBLE_MEMBER", "INVISIBLE_REFERENCE")
 fun <T> assertStaticTypeIs(@Suppress("UNUSED_PARAMETER") value: @kotlin.internal.NoInfer T) {}

libraries/stdlib/test/text/StringBuilderTest.kt

@@ -5,7 +5,9 @@
 
 package test.text
 
-import test.testOnJvm
+import test.TestPlatform
+import test.testOnlyOn
+import test.testExceptOn
 import kotlin.random.Random
 import kotlin.test.*
 import kotlin.text.*
@@ -39,11 +41,11 @@ class StringBuilderTest {
     fun deprecatedAppend() {
         val chars = charArrayOf('a', 'b', 'c', 'd')
         val sb = StringBuilder()
-        testOnJvm {
+        testOnlyOn(TestPlatform.Jvm) {
             sb.append(chars, 1, 2) // Should fail after KT-15220 gets fixed
             assertEquals("bc", sb.toString())
         }
-        if (sb.isEmpty()) {
+        testExceptOn(TestPlatform.Jvm) {
             assertFailsWith<NotImplementedError> {
                 sb.append(chars, 1, 2)
             }
@@ -256,8 +258,9 @@ class StringBuilderTest {
     @Test
     @Suppress("DEPRECATION")
     fun capacityTest() {
-//        assertEquals(100, StringBuilder(100).capacity()) // not implemented in JS
-
+        testExceptOn(TestPlatform.Js) {
+            assertEquals(100, StringBuilder(100).capacity()) // not implemented in JS
+        }
         StringBuilder("string builder from string capacity test").let { sb ->
             assertTrue(sb.capacity() >= sb.length)
         }
@@ -270,7 +273,9 @@ class StringBuilderTest {
             sb.ensureCapacity(1)
             assertTrue(sb.capacity() >= sb.length)
             sb.ensureCapacity(sb.length * 10)
-//            assertTrue(sb.capacity() >= sb.length * 10) // not implemented in JS
+            testExceptOn(TestPlatform.Js) {
+                assertTrue(sb.capacity() >= sb.length * 10) // not implemented in JS
+            }
         }
     }
 

libraries/stdlib/wasm/test/testUtils.kt

@@ -12,9 +12,7 @@ public actual fun assertTypeEquals(expected: Any?, actual: Any?) {
     assertEquals(expected?.let { it::class }, actual?.let { it::class })
 }
 
-
-public actual fun testOnJvm(action: () -> Unit) { }
-public actual fun testOnJs(action: () -> Unit) { }
+public actual val TestPlatform.Companion.current: TestPlatform get() = TestPlatform.Wasm
 
 // TODO: See KT-24975
 public actual val isFloat32RangeEnforced: Boolean = false