test: add a test for useNavigation

src/__tests__/useNavigation.test.tsx

@@ -0,0 +1,48 @@
+import * as React from 'react';
+import { render } from 'react-native-testing-library';
+import useNavigationBuilder from '../useNavigationBuilder';
+import useNavigation from '../useNavigation';
+import NavigationContainer from '../NavigationContainer';
+import Screen from '../Screen';
+import MockRouter from './__fixtures__/MockRouter';
+
+it('gets navigation prop from context', () => {
+  expect.assertions(1);
+
+  const TestNavigator = (props: any): any => {
+    const { state, descriptors } = useNavigationBuilder(MockRouter, props);
+
+    return state.routes.map(route => descriptors[route.key].render());
+  };
+
+  const Test = () => {
+    const navigation = useNavigation();
+
+    expect(navigation.navigate).toBeDefined();
+
+    return null;
+  };
+
+  render(
+    <NavigationContainer>
+      <TestNavigator>
+        <Screen name="foo" component={Test} />
+      </TestNavigator>
+    </NavigationContainer>
+  );
+});
+
+it('throws if called outside a navigation context', () => {
+  expect.assertions(1);
+
+  const Test = () => {
+    // eslint-disable-next-line react-hooks/rules-of-hooks
+    expect(() => useNavigation()).toThrow(
+      "We couldn't find a navigation object. Is your component inside a navigator?"
+    );
+
+    return null;
+  };
+
+  render(<Test />);
+});