test: add create_out_transition test

src/runtime/internal/transitions.ts

@@ -232,7 +232,7 @@ export function create_out_transition(node: Element & ElementCSSInlineStyle, fn:
 	}
 
 	return {
-		end(reset) {
+		end(reset: boolean) {
 			if (reset && config?.tick) {
 				config.tick(1, 0);
 			}

test/dom/index.ts

@@ -19,7 +19,7 @@ describe('dom', () => {
 		describe('when parentNode does not exist', () => {
 			it('should not throw an exception', () => {
 				const childWithoutParent = document.createElement('div');
-        let error = null;
+        let error: Error | null = null;
 
         try {
           detach(childWithoutParent);

test/transitions/index.ts

@@ -0,0 +1,49 @@
+import * as assert from 'assert';
+import { create_out_transition, group_outros } from 'svelte/internal';
+import { TransitionConfig } from 'svelte/transition';
+
+declare const global: any;
+
+describe('transitions', () => {
+  let originalRequestAnimationFrame: () => void;
+
+  before(() => {
+    originalRequestAnimationFrame = global.requestAnimationFrame;
+    global.requestAnimationFrame = cb => cb();
+  });
+
+  after(() => {
+    global.requestAnimationFrame = originalRequestAnimationFrame;
+  });
+
+  beforeEach(() => {
+    group_outros();
+  });
+  
+	describe('create_out_transition', () => {
+		describe('when then transition function returns undefined', () => {
+			describe('when calling the end function with reset param equals to true', () => {
+				it('should not throw an exception', () => {
+					const node = document.createElement('div');
+					const transitionConfig: TransitionConfig = {
+						duration: 0
+					};
+					const { end } = create_out_transition(
+						node,
+						() => undefined,
+						transitionConfig
+					);
+					let error: Error | null = null;
+
+					try {
+						end(true);
+					} catch (e) {
+						error = e;
+					}
+
+					assert.equal(error, null);
+				});
+			});
+		});
+	});
+});