test(frontend): add unit test coverage for extractErrorMessage

frontend/src/app/common/util/error.spec.ts

@@ -0,0 +1,64 @@
+/**
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you 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 { extractErrorMessage } from "./error";
+
+describe("extractErrorMessage", () => {
+  it("should return the message from an Error instance", () => {
+    const testError = new Error("error instance");
+    const result = extractErrorMessage(testError);
+    expect(result).toBe(testError.message);
+  });
+
+  it("should return the error string when error is a plain string", () => {
+    const testError = { error: "boom" };
+    const result = extractErrorMessage(testError);
+    expect(result).toBe(testError.error);
+  });
+
+  it("should return the nested message when error is an object with a message", () => {
+    const testError = { error: { message: "nested" } };
+    const result = extractErrorMessage(testError);
+    expect(result).toBe(testError.error.message);
+  });
+
+  it("should return the fallback message for when error is null", () => {
+    const testError = null;
+    const result = extractErrorMessage(testError);
+    expect(result).toBe("An unknown error occurred.");
+  });
+
+  it("should return the fallback message when error is a number", () => {
+    const testError = 123;
+    const result = extractErrorMessage(testError);
+    expect(result).toBe("An unknown error occurred.");
+  });
+
+  it("should return the fallback message when error is an empty object", () => {
+    const testError = {};
+    const result = extractErrorMessage(testError);
+    expect(result).toBe("An unknown error occurred.");
+  });
+
+  it("should return the fallback message when error key value is neither a string nor an object with a message", () => {
+    const testError = { error: 123 };
+    const result = extractErrorMessage(testError);
+    expect(result).toBe("An unknown error occurred.");
+  });
+});