react-native-safe-area-context/src/__tests__/initialWindowMetrics-test.tsx

import { UIManager } from 'react-native';
import { Metrics } from '../SafeArea.types';

describe('initialWindowMetrics', () => {
  it('is null when no view config is available', () => {
    jest.resetModules();
    expect(require('../initialWindowMetrics').initialWindowMetrics).toBe(null);
  });

  it('it uses the constant provided by the view config', () => {
    jest.resetModules();
    const testMetrics: Metrics = {
      insets: {
        top: 20,
        left: 0,
        right: 0,
        bottom: 0,
      },
      frame: {
        x: 0,
        y: 0,
        height: 100,
        width: 100,
      },
    };
    UIManager.getViewManagerConfig = jest.fn((name) => {
      if (name === 'RNCSafeAreaView') {
        return {
          Commands: {},
          Constants: {
            initialWindowMetrics: testMetrics,
          },
        };
      }
      return { Commands: {} };
    });

    expect(require('../index').initialWindowMetrics).toBe(testMetrics);
    expect(UIManager.getViewManagerConfig).toBeCalledWith('RNCSafeAreaView');
  });
});