Merge pull request #517 from arkivanov/add-Single-asPromise-extension

Add Single.asPromise() extension

reaktive/src/jsMain/kotlin/com/badoo/reaktive/single/AsPromise.kt

@@ -0,0 +1,8 @@
+package com.badoo.reaktive.single
+
+import kotlin.js.Promise
+
+fun <T> Single<T>.asPromise(): Promise<T> =
+    Promise { resolve, reject ->
+        subscribe(onSuccess = resolve, onError = reject)
+    }

reaktive/src/jsTest/kotlin/com/badoo/reaktive/single/AsPromiseTest.kt

@@ -0,0 +1,30 @@
+package com.badoo.reaktive.single
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+import kotlin.test.assertSame
+
+class AsPromiseTest {
+
+    @Test
+    fun resolves_non_null_value(): dynamic =
+        singleOf(1)
+            .asPromise()
+            .then { assertEquals(1, it) }
+
+    @Test
+    fun resolves_null_value(): dynamic =
+        singleOf<Int?>(null)
+            .asPromise()
+            .then { assertEquals(null, it) }
+
+    @Test
+    fun rejects(): dynamic {
+        val error = Exception()
+
+        return singleOfError<Nothing>(error)
+            .asPromise()
+            .catch { it }
+            .then { assertSame(error, it) }
+    }
+}