fix parallel to take a function

Author: mmalerba

src/cdk/testing/change-detection.ts

@@ -104,9 +104,9 @@ export async function manualChangeDetection<T>(fn: () => Promise<T>) {
  * Resolves the given list of async values in parallel (i.e. via Promise.all) while batching change
  * detection over the entire operation such that change detection occurs exactly once before
  * resolving the values and once after.
- * @param values The async values to resolve in parallel with batched change detection.
+ * @param values A getter for the async values to resolve in parallel with batched change detection.
  * @return The resolved values.
  */
-export async function parallel<T>(values: Iterable<T | PromiseLike<T>>) {
-  return batchChangeDetection(() => Promise.all(values), true);
+export async function parallel<T>(values: () => Iterable<T | PromiseLike<T>>) {
+  return batchChangeDetection(() => Promise.all(values()), true);
 }

src/cdk/testing/component-harness.ts

@@ -490,7 +490,7 @@ export class HarnessPredicate<T extends ComponentHarness> {
     if (harnesses.length === 0) {
       return [];
     }
-    const results = await parallel(harnesses.map(h => this.evaluate(h)));
+    const results = await parallel(() => harnesses.map(h => this.evaluate(h)));
     return harnesses.filter((_, i) => results[i]);
   }
 
@@ -501,7 +501,7 @@ export class HarnessPredicate<T extends ComponentHarness> {
    *   and resolves to false otherwise.
    */
   async evaluate(harness: T): Promise<boolean> {
-    const results = await parallel(this._predicates.map(p => p(harness)));
+    const results = await parallel(() => this._predicates.map(p => p(harness)));
     return results.reduce((combined, current) => combined && current, true);
   }
 

src/cdk/testing/harness-environment.ts

@@ -166,7 +166,7 @@ export abstract class HarnessEnvironment<E> implements HarnessLoader, LocatorFac
     const skipSelectorCheck = (elementQueries.length === 0 && harnessTypes.size === 1) ||
         harnessQueries.length === 0;
 
-    const perElementMatches = await parallel(rawElements.map(async rawElement => {
+    const perElementMatches = await parallel(() => rawElements.map(async rawElement => {
       const testElement = this.createTestElement(rawElement);
       const allResultsForElement = await Promise.all(
           // For each query, get `null` if it doesn't match, or a `TestElement` or

src/cdk/testing/test-harnesses.md

@@ -188,7 +188,7 @@ can read multiple properties from a harness with `parallel`:
 it('reads properties in parallel', async () => {
   const checkboxHarness = loader.getHarness(MyCheckboxHarness);
   // Read the checked and intermediate properties simultaneously.
-  const [checked, indeterminate] = await parallel([
+  const [checked, indeterminate] = await parallel(() => [
     checkboxHarness.isChecked(),
     checkboxHarness.isIndeterminate()
   ]);

src/cdk/testing/tests/testbed.spec.ts

@@ -99,19 +99,21 @@ describe('TestbedHarnessEnvironment', () => {
         const harness =
             await TestbedHarnessEnvironment.harnessForFixture(fixture, MainComponentHarness);
 
-        // Chain together our promises to ensure the before clause runs first and the after clause
-        // runs last.
-        const before =
-            Promise.resolve().then(() => expect(detectChangesSpy).toHaveBeenCalledTimes(1));
-        const actions = before.then(() => Promise.all(Array.from({length: 5},
-            () => harness.button().then(b => b.click()))));
-        const after = actions.then(() => expect(detectChangesSpy).toHaveBeenCalledTimes(1));
-
         // Run them in "parallel" (though the order is guaranteed because of how we constructed the
         // promises.
         detectChangesSpy.calls.reset();
         expect(detectChangesSpy).toHaveBeenCalledTimes(0);
-        await parallel<unknown>([before, actions, after]);
+        await parallel<unknown>(() => {
+          // Chain together our promises to ensure the before clause runs first and the after clause
+          // runs last.
+          const before =
+              Promise.resolve().then(() => expect(detectChangesSpy).toHaveBeenCalledTimes(1));
+          const actions = before.then(() => Promise.all(Array.from({length: 5},
+              () => harness.button().then(b => b.click()))));
+          const after = actions.then(() => expect(detectChangesSpy).toHaveBeenCalledTimes(1));
+
+          return [before, actions, after];
+        });
         expect(detectChangesSpy).toHaveBeenCalledTimes(2);
       });
 
@@ -121,7 +123,7 @@ describe('TestbedHarnessEnvironment', () => {
             await TestbedHarnessEnvironment.harnessForFixture(fixture, MainComponentHarness);
         detectChangesSpy.calls.reset();
         await manualChangeDetection(() => parallel(
-            Array.from({length: 5}, () => harness.button().then(b => b.click()))));
+            () => Array.from({length: 5}, () => harness.button().then(b => b.click()))));
         expect(detectChangesSpy).toHaveBeenCalledTimes(0);
       });
     });

tools/public_api_guard/cdk/testing.d.ts

@@ -124,7 +124,7 @@ export interface ModifierKeys {
     shift?: boolean;
 }
 
-export declare function parallel<T>(values: Iterable<T | PromiseLike<T>>): Promise<T[]>;
+export declare function parallel<T>(values: () => Iterable<T | PromiseLike<T>>): Promise<T[]>;
 
 export declare function stopHandlingAutoChangeDetectionStatus(): void;