🚧 (canal) Render first page by default

Author: tpucci

src/__tests__/__snapshots__/canal.test.tsx.snap

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+// Jest Snapshot v1, https://goo.gl/fbAQLP
+
+exports[`canal renders the first page when mounted 1`] = `<View />`;

src/__tests__/canal.test.ts

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+import React from 'react';
+import { View } from 'react-native';
+import TestRenderer from 'react-test-renderer';
+
+import { canal } from '../canal';
+
+describe('canal', () => {
+  it('throws an error if first arg is not a Component', () => {
+    try {
+      canal('aaa');
+    } catch (error) {
+      expect(error.message).toBe(
+        '`canal` expects its first argument to be a React component. Received type: string'
+      );
+    }
+    expect.assertions(1);
+  });
+
+  it('renders the first page when mounted', () => {
+    const Canal = canal(View);
+    const testRenderer = TestRenderer.create(<Canal />);
+    expect(testRenderer.toJSON()).toMatchSnapshot();
+  });
+});

src/__tests__/canal.test.tsx

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+import React, { ComponentType, FunctionComponent } from 'react';
+
+export const canal = (Page: ComponentType): FunctionComponent => {
+  if (!(React.isValidElement(Page) || typeof Page === 'function')) {
+    throw new Error(
+      `\`canal\` expects its first argument to be a React component. Received type: ${typeof Page}`
+    );
+  }
+  return () => <Page />;
+};