feat(material/tabs/testing): polish harness API

src/material/tabs/testing/BUILD.bazel

@@ -26,6 +26,7 @@ ng_test_library(
     deps = [
         ":testing",
         "//src/cdk/testing",
+        "//src/cdk/private/testing",
         "//src/cdk/testing/testbed",
         "//src/material/tabs",
         "@npm//@angular/forms",

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

@@ -1,3 +1,4 @@
+import {expectAsyncError} from '@angular/cdk/private/testing';
 import {HarnessLoader} from '@angular/cdk/testing';
 import {TestbedHarnessEnvironment} from '@angular/cdk/testing/testbed';
 import {Component} from '@angular/core';
@@ -51,6 +52,26 @@ export function runHarnessTests(
     expect(tabs.length).toBe(3);
   });
 
+  it('should be able to get filtered tabs', async () => {
+    const tabGroup = await loader.getHarness(tabGroupHarness);
+    const tabs = await tabGroup.getTabs({label: 'Third'});
+    expect(tabs.length).toBe(1);
+    expect(await tabs[0].getLabel()).toBe('Third');
+  });
+
+  it('should be able to select tab from tab-group', async () => {
+    const tabGroup = await loader.getHarness(tabGroupHarness);
+    expect(await (await tabGroup.getSelectedTab()).getLabel()).toBe('First');
+    await tabGroup.selectTab({label: 'Second'});
+    expect(await (await tabGroup.getSelectedTab()).getLabel()).toBe('Second');
+  });
+
+  it('should throw error when attempting to select invalid tab', async () => {
+    const tabGroup = await loader.getHarness(tabGroupHarness);
+    await expectAsyncError(() => tabGroup.selectTab({label: 'Fake'}),
+        /Error: Cannot find mat-tab matching {"label":"Fake"}/);
+  });
+
   it('should be able to get label of tabs', async () => {
     const tabGroup = await loader.getHarness(tabGroupHarness);
     const tabs = await tabGroup.getTabs();
@@ -78,13 +99,9 @@ export function runHarnessTests(
   it('should be able to get content element of active tab', async () => {
     const tabGroup = await loader.getHarness(tabGroupHarness);
     const tabs = await tabGroup.getTabs();
-    expect(await (await tabs[0].getContentElement()).text()).toBe('Content 1');
-  });
-
-  it('should be able to get content element of active tab', async () => {
-    const tabGroup = await loader.getHarness(tabGroupHarness);
-    const tabs = await tabGroup.getTabs();
-    expect(await (await tabs[0].getContentElement()).text()).toBe('Content 1');
+    const contentSelector = await tabs[0].getSelectorForContent();
+    const contentEl = document.querySelector(contentSelector) as HTMLElement;
+    expect(contentEl.innerText.trim()).toBe('Content 1');
   });
 
   it('should be able to get disabled state of tab', async () => {

src/material/tabs/testing/tab-group-harness.ts

@@ -7,7 +7,7 @@
  */
 
 import {ComponentHarness, HarnessPredicate} from '@angular/cdk/testing';
-import {TabGroupHarnessFilters} from './tab-harness-filters';
+import {TabGroupHarnessFilters, TabHarnessFilters} from './tab-harness-filters';
 import {MatTabHarness} from './tab-harness';
 
 /**
@@ -34,11 +34,9 @@ export class MatTabGroupHarness extends ComponentHarness {
         });
   }
 
-  private _tabs = this.locatorForAll(MatTabHarness);
-
   /** Gets all tabs of the tab group. */
-  async getTabs(): Promise<MatTabHarness[]> {
-    return this._tabs();
+  async getTabs(filter: TabHarnessFilters = {}): Promise<MatTabHarness[]> {
+    return this.locatorForAll(MatTabHarness.with(filter))();
   }
 
   /** Gets the selected tab of the tab group. */
@@ -52,4 +50,13 @@ export class MatTabGroupHarness extends ComponentHarness {
     }
     throw new Error('No selected tab could be found.');
   }
+
+  /** Selects a tab in this tab group. */
+  async selectTab(filter: TabHarnessFilters = {}): Promise<void> {
+    const tabs = await this.getTabs(filter);
+    if (!tabs.length) {
+      throw Error(`Cannot find mat-tab matching ${JSON.stringify(filter)}`);
+    }
+    await tabs[0].select();
+  }
 }

src/material/tabs/testing/tab-harness-filters.ts

@@ -7,7 +7,9 @@
  */
 import {BaseHarnessFilters} from '@angular/cdk/testing';
 
-export interface TabHarnessFilters extends BaseHarnessFilters {}
+export interface TabHarnessFilters extends BaseHarnessFilters {
+  label?: string | RegExp;
+}
 
 export interface TabGroupHarnessFilters extends BaseHarnessFilters {
   selectedTabLabel?: string | RegExp;

src/material/tabs/testing/tab-harness.ts

@@ -20,7 +20,9 @@ export class MatTabHarness extends ComponentHarness {
    * Gets a `HarnessPredicate` that can be used to search for a tab with specific attributes.
    */
   static with(options: TabHarnessFilters = {}): HarnessPredicate<MatTabHarness> {
-    return new HarnessPredicate(MatTabHarness, options);
+    return new HarnessPredicate(MatTabHarness, options)
+        .addOption('label', options.label,
+            (harness, label) => HarnessPredicate.stringMatches(harness.getLabel(), label));
   }
 
   private _rootLocatorFactory = this.documentRootLocatorFactory();
@@ -40,15 +42,6 @@ export class MatTabHarness extends ComponentHarness {
     return (await this.host()).getAttribute('aria-labelledby');
   }
 
-  /**
-   * Gets the content element of the given tab. Note that the element will be empty
-   * until the tab is selected. This is an implementation detail of the tab-group
-   * in order to avoid rendering of non-active tabs.
-   */
-  async getContentElement(): Promise<TestElement> {
-    return this._rootLocatorFactory.locatorFor(`#${await this._getContentId()}`)();
-  }
-
   /** Whether the tab is selected. */
   async isSelected(): Promise<boolean> {
     const hostEl = await this.host();
@@ -69,10 +62,10 @@ export class MatTabHarness extends ComponentHarness {
     await (await this.host()).click();
   }
 
-  /** Gets the element id for the content of the current tab. */
-  private async _getContentId(): Promise<string> {
+  /** Gets a selector that can be used to locate the tab's content element. */
+  async getSelectorForContent(): Promise<string> {
     const hostEl = await this.host();
     // Tabs never have an empty "aria-controls" attribute.
-    return (await hostEl.getAttribute('aria-controls'))!;
+    return '#' + await hostEl.getAttribute('aria-controls');
   }
 }