Address PR review feedback on breadcrumbs scaffolding

- Add LumoInjectionMixin to <vaadin-breadcrumbs> and
  <vaadin-breadcrumbs-item> for Lumo theming
- Switch registry tests to the tagName.toLowerCase() pattern
- Replace shadowRoot tests with snapshot tests under test/dom/
- Add breadcrumbs-item.test.js stub for item-specific logic

Author: Artur-

packages/breadcrumbs/src/vaadin-breadcrumbs-item.js

@@ -7,6 +7,7 @@ import { html, LitElement } from 'lit';
 import { defineCustomElement } from '@vaadin/component-base/src/define.js';
 import { ElementMixin } from '@vaadin/component-base/src/element-mixin.js';
 import { PolylitMixin } from '@vaadin/component-base/src/polylit-mixin.js';
+import { LumoInjectionMixin } from '@vaadin/vaadin-themable-mixin/lumo-injection-mixin.js';
 import { breadcrumbsItemStyles } from './styles/vaadin-breadcrumbs-item-base-styles.js';
 
 /**
@@ -16,7 +17,7 @@ import { breadcrumbsItemStyles } from './styles/vaadin-breadcrumbs-item-base-sty
  * @extends HTMLElement
  * @mixes ElementMixin
  */
-class BreadcrumbsItem extends ElementMixin(PolylitMixin(LitElement)) {
+class BreadcrumbsItem extends ElementMixin(PolylitMixin(LumoInjectionMixin(LitElement))) {
   static get is() {
     return 'vaadin-breadcrumbs-item';
   }

packages/breadcrumbs/src/vaadin-breadcrumbs.js

@@ -8,6 +8,7 @@ import { html, LitElement } from 'lit';
 import { defineCustomElement } from '@vaadin/component-base/src/define.js';
 import { ElementMixin } from '@vaadin/component-base/src/element-mixin.js';
 import { PolylitMixin } from '@vaadin/component-base/src/polylit-mixin.js';
+import { LumoInjectionMixin } from '@vaadin/vaadin-themable-mixin/lumo-injection-mixin.js';
 import { breadcrumbsStyles } from './styles/vaadin-breadcrumbs-base-styles.js';
 
 /**
@@ -18,7 +19,7 @@ import { breadcrumbsStyles } from './styles/vaadin-breadcrumbs-base-styles.js';
  * @extends HTMLElement
  * @mixes ElementMixin
  */
-class Breadcrumbs extends ElementMixin(PolylitMixin(LitElement)) {
+class Breadcrumbs extends ElementMixin(PolylitMixin(LumoInjectionMixin(LitElement))) {
   static get is() {
     return 'vaadin-breadcrumbs';
   }

packages/breadcrumbs/test/breadcrumbs-item.test.js

@@ -0,0 +1,31 @@
+import { expect } from '@vaadin/chai-plugins';
+import { fixtureSync } from '@vaadin/testing-helpers';
+import '../vaadin-breadcrumbs-item.js';
+
+window.Vaadin ??= {};
+window.Vaadin.featureFlags ??= {};
+window.Vaadin.featureFlags.breadcrumbsComponent = true;
+
+describe('vaadin-breadcrumbs-item', () => {
+  let item;
+
+  beforeEach(() => {
+    item = fixtureSync('<vaadin-breadcrumbs-item></vaadin-breadcrumbs-item>');
+  });
+
+  describe('custom element definition', () => {
+    let tagName;
+
+    beforeEach(() => {
+      tagName = item.tagName.toLowerCase();
+    });
+
+    it('should be defined in custom element registry', () => {
+      expect(customElements.get(tagName)).to.be.ok;
+    });
+
+    it('should have a valid static "is" getter', () => {
+      expect(customElements.get(tagName).is).to.equal(tagName);
+    });
+  });
+});

packages/breadcrumbs/test/breadcrumbs.test.js

@@ -1,30 +1,31 @@
 import { expect } from '@vaadin/chai-plugins';
-import { fixtureSync, nextRender } from '@vaadin/testing-helpers';
+import { fixtureSync } from '@vaadin/testing-helpers';
 import '../vaadin-breadcrumbs.js';
-import '../vaadin-breadcrumbs-item.js';
 
 window.Vaadin ??= {};
 window.Vaadin.featureFlags ??= {};
 window.Vaadin.featureFlags.breadcrumbsComponent = true;
 
 describe('vaadin-breadcrumbs', () => {
-  it('should register vaadin-breadcrumbs in the custom element registry', () => {
-    expect(customElements.get('vaadin-breadcrumbs')).to.be.ok;
-  });
+  let breadcrumbs;
 
-  it('should register vaadin-breadcrumbs-item in the custom element registry', () => {
-    expect(customElements.get('vaadin-breadcrumbs-item')).to.be.ok;
+  beforeEach(() => {
+    breadcrumbs = fixtureSync('<vaadin-breadcrumbs></vaadin-breadcrumbs>');
   });
 
-  it('should attach the breadcrumbs with a non-null shadowRoot', async () => {
-    const breadcrumbs = fixtureSync('<vaadin-breadcrumbs></vaadin-breadcrumbs>');
-    await nextRender();
-    expect(breadcrumbs.shadowRoot).to.not.be.null;
-  });
+  describe('custom element definition', () => {
+    let tagName;
+
+    beforeEach(() => {
+      tagName = breadcrumbs.tagName.toLowerCase();
+    });
+
+    it('should be defined in custom element registry', () => {
+      expect(customElements.get(tagName)).to.be.ok;
+    });
 
-  it('should attach the item with a non-null shadowRoot', async () => {
-    const item = fixtureSync('<vaadin-breadcrumbs-item></vaadin-breadcrumbs-item>');
-    await nextRender();
-    expect(item.shadowRoot).to.not.be.null;
+    it('should have a valid static "is" getter', () => {
+      expect(customElements.get(tagName).is).to.equal(tagName);
+    });
   });
 });

packages/breadcrumbs/test/dom/__snapshots__/breadcrumbs-item.test.snap.js

@@ -0,0 +1,9 @@
+/* @web/test-runner snapshot v1 */
+export const snapshots = {};
+
+snapshots["vaadin-breadcrumbs-item host default"] = 
+`<vaadin-breadcrumbs-item>
+</vaadin-breadcrumbs-item>
+`;
+/* end snapshot vaadin-breadcrumbs-item host default */
+

packages/breadcrumbs/test/dom/__snapshots__/breadcrumbs.test.snap.js

@@ -0,0 +1,9 @@
+/* @web/test-runner snapshot v1 */
+export const snapshots = {};
+
+snapshots["vaadin-breadcrumbs host default"] = 
+`<vaadin-breadcrumbs>
+</vaadin-breadcrumbs>
+`;
+/* end snapshot vaadin-breadcrumbs host default */
+

packages/breadcrumbs/test/dom/breadcrumbs-item.test.js

@@ -0,0 +1,28 @@
+import { expect } from '@vaadin/chai-plugins';
+import { fixtureSync, nextRender } from '@vaadin/testing-helpers';
+import '../../src/vaadin-breadcrumbs-item.js';
+
+window.Vaadin ??= {};
+window.Vaadin.featureFlags ??= {};
+window.Vaadin.featureFlags.breadcrumbsComponent = true;
+
+describe('vaadin-breadcrumbs-item', () => {
+  let item;
+
+  beforeEach(async () => {
+    item = fixtureSync('<vaadin-breadcrumbs-item></vaadin-breadcrumbs-item>');
+    await nextRender();
+  });
+
+  describe('host', () => {
+    it('default', async () => {
+      await expect(item).dom.to.equalSnapshot();
+    });
+  });
+
+  describe('shadow', () => {
+    it('default', async () => {
+      await expect(item).shadowDom.to.equalSnapshot();
+    });
+  });
+});

packages/breadcrumbs/test/dom/breadcrumbs.test.js

@@ -0,0 +1,28 @@
+import { expect } from '@vaadin/chai-plugins';
+import { fixtureSync, nextRender } from '@vaadin/testing-helpers';
+import '../../src/vaadin-breadcrumbs.js';
+
+window.Vaadin ??= {};
+window.Vaadin.featureFlags ??= {};
+window.Vaadin.featureFlags.breadcrumbsComponent = true;
+
+describe('vaadin-breadcrumbs', () => {
+  let breadcrumbs;
+
+  beforeEach(async () => {
+    breadcrumbs = fixtureSync('<vaadin-breadcrumbs></vaadin-breadcrumbs>');
+    await nextRender();
+  });
+
+  describe('host', () => {
+    it('default', async () => {
+      await expect(breadcrumbs).dom.to.equalSnapshot();
+    });
+  });
+
+  describe('shadow', () => {
+    it('default', async () => {
+      await expect(breadcrumbs).shadowDom.to.equalSnapshot();
+    });
+  });
+});