diff --git a/packages/frontend-plugin-api/src/wiring/resolveExtensionDefinition.test.ts b/packages/frontend-plugin-api/src/wiring/resolveExtensionDefinition.test.ts
new file mode 100644
index 0000000000..202c513aa2
--- /dev/null
+++ b/packages/frontend-plugin-api/src/wiring/resolveExtensionDefinition.test.ts
@@ -0,0 +1,48 @@
+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import { ExtensionDefinition } from './createExtension';
+import { resolveExtensionDefinition } from './resolveExtensionDefinition';
+
+describe('resolveExtensionDefinition', () => {
+  it.each([
+    [{ namespace: 'ns' }, 'ns'],
+    [{ namespace: 'ns', name: 'n' }, 'ns/n'],
+    [{ kind: 'k', namespace: 'ns' }, 'k:ns'],
+    [{ kind: 'k', namespace: 'ns', name: 'n' }, 'k:ns/n'],
+  ])(`should resolve extension IDs %s`, (definition, expected) => {
+    const resolved = resolveExtensionDefinition(
+      definition as ExtensionDefinition<unknown>,
+    );
+    expect(resolved.id).toBe(expected);
+  });
+
+  it('should fail to resolve extension ID without namespace', () => {
+    expect(() =>
+      resolveExtensionDefinition({
+        kind: 'k',
+        name: 'n',
+      } as ExtensionDefinition<unknown>),
+    ).toThrow(
+      'Extension must declare an explicit namespace as it could not be resolved from context, name=n kind=k',
+    );
+    expect(() =>
+      resolveExtensionDefinition({} as ExtensionDefinition<unknown>),
+    ).toThrow(
+      'Extension must declare an explicit namespace as it could not be resolved from context, name=undefined kind=undefined',
+    );
+  });
+});