add more tests

src/components/Loader/Loader.test.tsx

@@ -0,0 +1,14 @@
+import React from "react";
+import { screen, render } from "@testing-library/react";
+
+import Loader from "./Loader";
+
+const setup = () => render(<Loader />);
+
+describe("Loader", () => {
+  it("should display loading message", () => {
+    setup();
+    const loadingText = screen.getByText("Loading...");
+    expect(loadingText).toBeInTheDocument();
+  });
+});

src/components/SiteHeader/SiteHeader.test.tsx

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+import React from "react";
+import { screen } from "@testing-library/react";
+import renderConnected from "utilities/test/renderConnected";
+
+import SiteHeader from "./SiteHeader";
+
+const setup = () =>
+  renderConnected({
+    ui: <SiteHeader />,
+    initialState: {
+      userProfile: {
+        username: "Steve",
+      },
+    },
+  });
+
+describe("SiteHeader", () => {
+  it("should display logo", () => {
+    setup();
+    const logoImg = screen.getByAltText("Company name");
+    expect(logoImg).toBeInTheDocument();
+  });
+});

src/state/userProfile/selectors.test.ts

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+import { getUsername } from "./selectors";
+
+import { RootState } from "../rootReducer";
+
+describe("UserProfile selectors", () => {
+  describe("getUsername", () => {
+    it("should return username", () => {
+      const state: RootState = {
+        userProfile: {
+          username: "Steve",
+        },
+      };
+      expect(getUsername(state)).toBe("Steve");
+    });
+  });
+});