refactor(material/list): make test harness base classes abstract and cleanup

Makes base classes for the list and item harnesses abstract based
on review feedback for the equivalent MDC list harness.

Also cleans up logic for retrieving options of a selection list. The
current logic seemed to use a non-idiomatic way of flattening items.
We switch that to an idiomatic reduce which is more readable.

Author: devversion

src/material-experimental/mdc-list/testing/list-harness.spec.ts

@@ -15,5 +15,5 @@ describe('MDC-based list harnesses', () => {
   runHarnessTests(
       MatListModule, MatListHarness as any, MatActionListHarness as any, MatNavListHarness as any,
       MatSelectionListHarness as any, MatListItemHarnessBase as any, MatSubheaderHarness as any,
-      MatDividerHarness);
+      MatDividerHarness, {content: MatListItemSection.CONTENT});
 });

src/material/list/testing/list-harness-base.ts

@@ -31,7 +31,7 @@ export interface ListSection<I> {
  * @template F The filter type used filter list item harness of type `C`.
  * @docs-private
  */
-export class MatListHarnessBase
+export abstract class MatListHarnessBase
     <
       T extends (ComponentHarnessConstructor<C> & {with: (options?: F) => HarnessPredicate<C>}),
       C extends ComponentHarness,

src/material/list/testing/list-harness.spec.ts

@@ -4,11 +4,16 @@ import {MatActionListHarness} from './action-list-harness';
 import {MatListHarness} from './list-harness';
 import {MatNavListHarness} from './nav-list-harness';
 import {MatSelectionListHarness} from './selection-list-harness';
-import {MatListItemHarnessBase, MatSubheaderHarness} from './list-item-harness-base';
+import {
+  MatListItemHarnessBase,
+  MatListItemSection,
+  MatSubheaderHarness
+} from './list-item-harness-base';
 import {runHarnessTests} from './shared.spec';
 
 describe('Non-MDC-based list harnesses', () => {
   runHarnessTests(
       MatListModule, MatListHarness, MatActionListHarness, MatNavListHarness,
-      MatSelectionListHarness, MatListItemHarnessBase, MatSubheaderHarness, MatDividerHarness);
+      MatSelectionListHarness, MatListItemHarnessBase, MatSubheaderHarness, MatDividerHarness,
+      {content: MatListItemSection.CONTENT});
 });

src/material/list/testing/list-item-harness-base.ts

@@ -59,7 +59,9 @@ export const enum MatListItemSection {
  * Shared behavior among the harnesses for the various `MatListItem` flavors.
  * @docs-private
  */
-export class MatListItemHarnessBase extends ContentContainerComponentHarness<MatListItemSection> {
+export abstract class MatListItemHarnessBase
+    extends ContentContainerComponentHarness<MatListItemSection> {
+
   private _lines = this.locatorForAll('.mat-line');
   private _avatar = this.locatorForOptional(avatarSelector);
   private _icon = this.locatorForOptional(iconSelector);

src/material/list/testing/selection-list-harness.ts

@@ -62,8 +62,9 @@ export class MatSelectionListHarness extends MatListHarnessBase<
     if (!filters.length) {
       return this.getItems();
     }
-    return ([] as MatListOptionHarness[]).concat(...await Promise.all(
-        filters.map(filter => this.locatorForAll(MatListOptionHarness.with(filter))())));
+    const matches = await Promise.all(
+      filters.map(filter => this.locatorForAll(MatListOptionHarness.with(filter))()));
+    return matches.reduce((result, current) => [...result, ...current], []);
   }
 }
 

src/material/list/testing/shared.spec.ts

@@ -13,7 +13,11 @@ import {MatActionListHarness, MatActionListItemHarness} from './action-list-harn
 import {MatListHarness, MatListItemHarness} from './list-harness';
 import {MatListHarnessBase} from './list-harness-base';
 import {BaseListItemHarnessFilters} from './list-harness-filters';
-import {MatListItemHarnessBase, MatSubheaderHarness} from './list-item-harness-base';
+import {
+  MatListItemHarnessBase,
+  MatListItemSection,
+  MatSubheaderHarness
+} from './list-item-harness-base';
 import {MatNavListHarness, MatNavListItemHarness} from './nav-list-harness';
 import {MatListOptionHarness, MatSelectionListHarness} from './selection-list-harness';
 
@@ -33,7 +37,8 @@ function runBaseListFunctionalityTests<
     },
     listItemHarnessBase: typeof MatListItemHarnessBase,
     subheaderHarness: typeof MatSubheaderHarness,
-    dividerHarness: typeof MatDividerHarness) {
+    dividerHarness: typeof MatDividerHarness,
+    selectors: {content: string}) {
   describe('base list functionality', () => {
     let simpleListHarness: L;
     let emptyListHarness: L;
@@ -183,6 +188,13 @@ function runBaseListFunctionalityTests<
       const childHarness = await items[1].getHarness(TestItemContentHarness);
       expect(childHarness).not.toBeNull();
     });
+
+    it('should be able to get content harness loader of list item', async () => {
+      const items = await simpleListHarness.getItems();
+      expect(items.length).toBe(3);
+      const loader = await items[1].getChildLoader(selectors.content as MatListItemSection);
+      await expectAsync(loader.getHarness(TestItemContentHarness)).toBeResolved();
+    });
   });
 }
 
@@ -199,17 +211,18 @@ export function runHarnessTests(
     selectionListHarness: typeof MatSelectionListHarness,
     listItemHarnessBase: typeof MatListItemHarnessBase,
     subheaderHarness: typeof MatSubheaderHarness,
-    dividerHarness: typeof MatDividerHarness) {
+    dividerHarness: typeof MatDividerHarness,
+    selectors: {content: string}) {
   describe('MatListHarness', () => {
     runBaseListFunctionalityTests<MatListHarness, MatListItemHarness>(
         ListHarnessTest, listModule, listHarness, listItemHarnessBase, subheaderHarness,
-        dividerHarness);
+        dividerHarness, selectors);
   });
 
   describe('MatActionListHarness', () => {
     runBaseListFunctionalityTests<MatActionListHarness, MatActionListItemHarness>(
         ActionListHarnessTest, listModule, actionListHarness, listItemHarnessBase, subheaderHarness,
-        dividerHarness);
+        dividerHarness, selectors);
 
     describe('additional functionality', () => {
       let harness: MatActionListHarness;
@@ -244,7 +257,7 @@ export function runHarnessTests(
   describe('MatNavListHarness', () => {
     runBaseListFunctionalityTests<MatNavListHarness, MatNavListItemHarness>(
         NavListHarnessTest, listModule, navListHarness, listItemHarnessBase, subheaderHarness,
-        dividerHarness);
+        dividerHarness, selectors);
 
     describe('additional functionality', () => {
       let harness: MatNavListHarness;
@@ -290,7 +303,7 @@ export function runHarnessTests(
   describe('MatSelectionListHarness', () => {
     runBaseListFunctionalityTests<MatSelectionListHarness, MatListOptionHarness>(
         SelectionListHarnessTest, listModule, selectionListHarness, listItemHarnessBase,
-        subheaderHarness, dividerHarness);
+        subheaderHarness, dividerHarness, selectors);
 
     describe('additional functionality', () => {
       let harness: MatSelectionListHarness;