Factor out post-login splash screen to a new component (#12103)

* Factor out post-login splash screen to a new component

* Move CSS classes to per-component file

* Rename CSS classes

... to reflect the component that uses them

* code review

test/components/structures/auth/LoginSplashView-test.tsx

@@ -0,0 +1,49 @@
+/*
+Copyright 2024 The Matrix.org Foundation C.I.C.
+
+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 { render, RenderResult } from "@testing-library/react";
+import React, { ComponentProps } from "react";
+
+import { LoginSplashView } from "../../../../src/components/structures/auth/LoginSplashView";
+
+describe("<LoginSplashView />", () => {
+    function getComponent(props: Partial<ComponentProps<typeof LoginSplashView>> = {}): RenderResult {
+        const defaultProps = {
+            onLogoutClick: () => {},
+            syncError: null,
+        };
+        return render(<LoginSplashView {...defaultProps} {...props} />);
+    }
+
+    it("Renders a spinner", () => {
+        const rendered = getComponent();
+        expect(rendered.getByTestId("spinner")).toBeInTheDocument();
+        expect(rendered.asFragment()).toMatchSnapshot();
+    });
+
+    it("Renders an error message", () => {
+        const rendered = getComponent({ syncError: new Error("boohoo") });
+        expect(rendered.asFragment()).toMatchSnapshot();
+    });
+
+    it("Calls onLogoutClick", () => {
+        const onLogoutClick = jest.fn();
+        const rendered = getComponent({ onLogoutClick });
+        expect(onLogoutClick).not.toHaveBeenCalled();
+        rendered.getByRole("button", { name: "Logout" }).click();
+        expect(onLogoutClick).toHaveBeenCalled();
+    });
+});