Correctly mocked useNavigate Hook for Donors.test (#237)

Refers to #231 
Earlier due to issues with useNavigate tests were failing , which have
now been refactored.
A Few of the older tests have been refactored , new tests for donorview
to be written soon.
Raising PR to put in a donor page tests back in the repo . Also removing
donors.txt from repo

frontend/src/__tests__/donors.test.tsx

@@ -0,0 +1,71 @@
+import React from "react";
+import { render, fireEvent, screen } from "@testing-library/react";
+import { useNavigate } from "react-router-dom";
+import Donor from "../pages/donors";
+
+jest.mock("react-router-dom", () => ({
+    useNavigate: jest.fn(),
+}));
+
+describe("Donor component", () => {
+    it("Checks Rendering of donor page by checking Donor List Text Presence", () => {
+        const navigate = jest.fn();
+        (useNavigate as jest.Mock).mockReturnValue(navigate);
+        const { getByText } = render(<Donor />);
+        const heading = getByText(/Donor List/i);
+        expect(heading).toBeInTheDocument();
+    });
+    it("renders Add Donor button", () => {
+        const navigate = jest.fn();
+        (useNavigate as jest.Mock).mockReturnValue(navigate);
+        const { getByText } = render(<Donor />);
+        const addButton = getByText(/Add Donor/i);
+        expect(addButton).toBeInTheDocument();
+    });
+    it("renders Lookup Donor button", () => {
+        const navigate = jest.fn();
+        (useNavigate as jest.Mock).mockReturnValue(navigate);
+        const { getByText } = render(<Donor />);
+        const addButton = getByText(/Lookup Donor/i);
+        expect(addButton).toBeInTheDocument();
+    });
+    it("displays an error message if the no email address is provided in the Email Address field of the add donor dialog", () => {
+        const navigate = jest.fn();
+        (useNavigate as jest.Mock).mockReturnValue(navigate);
+        const { getByRole, getByLabelText, getByText, queryByText } = render(
+            <Donor />
+        );
+        const addDonorButton = getByRole("button", { name: "Add Donor" });
+        fireEvent.click(addDonorButton);
+        const personID = getByLabelText("Person ID")
+        const emailInput = getByLabelText("Email");
+        const addButton = getByText("Add");
+        expect(addButton).toBeDisabled();
+        //First we put in dummy text
+        fireEvent.change(emailInput, { target: { value: "zyzz" } });
+        fireEvent.change(personID, { target: { value: "2" } });
+        //Removing the dummy text to initiate warning message
+        fireEvent.change(emailInput, { target: { value: "" } });
+        fireEvent.click(addButton);
+        expect(queryByText("Email is required")).toBeInTheDocument();
+    });
+    it("displays an error message if the email address is invalid in the add donor dialog", () => {
+        const navigate = jest.fn();
+        (useNavigate as jest.Mock).mockReturnValue(navigate);
+        const { getByRole, getByLabelText, getByText, queryByText } = render(
+            <Donor />
+        );
+        const addDonorButton = getByRole("button", { name: "Add Donor" });
+        fireEvent.click(addDonorButton);
+        const emailInput = getByLabelText("Email");
+        const addButton = getByText("Add");
+        //Add button should be initially disabled
+        expect(addButton).toBeDisabled();
+        //Entering an invalid email
+        fireEvent.change(emailInput, { target: { value: "invalid_email" } });
+        fireEvent.click(addButton);
+        //Error message should be displayed
+        expect(queryByText("Email is invalid")).toBeInTheDocument();
+    });
+
+});