[#121] added error handler and snackbar

__test__/features/Error/ErrorHandler.test.tsx

@@ -0,0 +1,35 @@
+import { EventErrorHandler } from "../../../src/components/Error/EventErrorHandler";
+
+describe("EventErrorHandler", () => {
+  it("calls the callback when a new error is reported", () => {
+    const handler = new EventErrorHandler();
+    const callback = jest.fn();
+
+    handler.setErrorCallback(callback);
+    handler.reportError("123", "Something broke");
+
+    expect(callback).toHaveBeenCalledWith(["Something broke"]);
+  });
+
+  it("does not duplicate errors for same eventId", () => {
+    const handler = new EventErrorHandler();
+    const callback = jest.fn();
+
+    handler.setErrorCallback(callback);
+    handler.reportError("A", "Error 1");
+    handler.reportError("A", "Error 1 again");
+
+    expect(callback).toHaveBeenCalledTimes(1);
+  });
+
+  it("clears errors properly", () => {
+    const handler = new EventErrorHandler();
+    const callback = jest.fn();
+
+    handler.setErrorCallback(callback);
+    handler.reportError("A", "Error 1");
+    handler.clearAll();
+
+    expect(callback).toHaveBeenLastCalledWith([]);
+  });
+});