test: add tests for warnUndefinedElement with hanbi for stubbing methods

package.json

@@ -133,6 +133,7 @@
     "eslint-plugin-promise": "^5.1.1",
     "eslint-plugin-regexp": "^1.5.1",
     "eslint-plugin-simple-import-sort": "^7.0.0",
+    "hanbi": "^1.0.1",
     "nano-staged": "^0.3.1",
     "typescript": "^4.5.2"
   },

src/__tests__/helpers/warn-undefined-element.test.ts

@@ -0,0 +1,30 @@
+import { expect } from '@open-wc/testing';
+import { stubMethod } from 'hanbi';
+
+import { warnUndefinedElement } from '../../helpers/warn-undefined-element';
+import { RootElement } from '../../root-element/root-element';
+
+const warn = stubMethod(console, 'warn');
+
+describe(warnUndefinedElement.name, () => {
+  const elementName = 'test-element' as const;
+  const elementName2 = 'test-element-2' as const;
+
+  afterEach(() => {
+    warn.reset();
+  });
+
+  it('does not warn defined element', () => {
+    globalThis.customElements.define(elementName, class A extends RootElement {});
+
+    warnUndefinedElement(elementName);
+
+    expect(warn.called).false;
+  });
+
+  it('warns undefined element', () => {
+    warnUndefinedElement(elementName2);
+
+    expect(warn.lastCall?.args).deep.equal([`${elementName2} is required`]);
+  });
+});