Component.test.tsx

describe("rendering", () => {
    let wrapper: ShallowWrapper;
    let props: Props;
    let Platform: PlatformStatic;
    beforeEach(() => {
      props = createTestProps({});
      wrapper = shallow(<LoginScreen {...props} />);
      Platform = require("react-native").Platform;
    });

    // ... other tests

    it("should render a <KeyboardAvoidingView />", () => {
      expect(wrapper.find("KeyboardAvoidingView")).toHaveLength(1);
    });

    describe("<KeyboardAvoidingView />'s behavior on iOS", () => {
      beforeEach(() => {
        Platform.OS = "ios";
      });

      it("should have a 'behavior' prop of 'padding'", () => {
        expect(wrapper.find("KeyboardAvoidingView").prop("behavior")).toBe("padding");
      });
    });

    describe("<KeyboardAvoidingView />'s behavior on Android", () => {
      beforeEach(() => {
        Platform.OS = "android";
      });

      it("should NOT have a behavior prop", () => {
        expect(wrapper.find("KeyboardAvoidingView").prop("behavior")).toBe(undefined);
      });
    });

    // ... more other tests