docs: in code guidelines, use vi.mocked (#10353)

* docs: use vi.mocked

Signed-off-by: Philippe Martin <phmartin@redhat.com>

* fix: remove unnecessary code

Signed-off-by: Philippe Martin <phmartin@redhat.com>

---------

Signed-off-by: Philippe Martin <phmartin@redhat.com>

CODE-GUIDELINES.md

@@ -0,0 +1,39 @@
+# Guidelines for Podman Desktop Code
+
+## Production code
+
+## Unit tests code
+
+### Use `vi.mocked`, not a generic `myFunctionMock`
+
+If you define a mock with `const myFunctionMock = vi.fn();` its type is `Mock<Procedure>`, which is a generic type.
+
+For example, do not write this, or Typescript won't be able to detect that you passed an object instead of a string to `mockResolvedValue`:
+
+```ts
+const windowMethodMock = vi.fn();
+
+Object.defineProperty(global, 'window', {
+  value: {
+    windowMethod: windowMethodMock,
+  },
+});
+
+test('...', () => {
+  windowMethodMock.mockResolvedValue({ msg: 'a string' }); // here, Typescript is not able to detect that the type is wrong
+});
+```
+
+Instead, you can write `vi.mocked(window.windowMethod).mock...`, and Typescript will check that you correctly pass a string to `mockResolvedValue`:
+
+```ts
+Object.defineProperty(global, 'window', {
+  value: {
+    windowMethod: vi.fn(),
+  },
+});
+
+test('...', () => {
+  vi.mocked(window.windowMethod).mockResolvedValue('a string');
+});
+```