chore: Add additional tests for undefined platform minification behav…

…ior. (#27515)

# Why

- Metro's platform minification plugin has undefined behavior where the
Platform module doesn't need to come from the `react-native` import,
this inadvertently resolves the need to add support for
`expo-modules-core`.
- I'll add a follow up PR to fork the Metro plugin and remove the many
additional passes used to support haste. Will also fix the extra case I
found where `.native` is left as-is even when bundling for web.

# Test Plan

- Added tests only

---------

Co-authored-by: Expo Bot <34669131+expo-bot@users.noreply.github.com>

packages/babel-preset-expo/CHANGELOG.md

@@ -13,6 +13,7 @@
 ### 💡 Others
 
 - Disable color in snapshot tests in CI. ([#27301](https://github.com/expo/expo/pull/27301) by [@EvanBacon](https://github.com/EvanBacon))
+- Add additional tests for undefined platform minification behavior. ([#27515](https://github.com/expo/expo/pull/27515) by [@EvanBacon](https://github.com/EvanBacon))
 - Upgrade `babel-plugin-react-native-web` for latest `react-native-web` aliases. ([#27214](https://github.com/expo/expo/pull/27214) by [@EvanBacon](https://github.com/EvanBacon))
 - Directly resolve plugins. ([#27041](https://github.com/expo/expo/pull/27041) by [@EvanBacon](https://github.com/EvanBacon))
 

packages/babel-preset-expo/src/__tests__/platform-shaking.test.ts

@@ -30,6 +30,62 @@ function stripReactNativeImport(code: string) {
     .replace('var _reactNative=require("react-native");', '');
 }
 
+it(`removes Platform module without import (undefined behavior)`, () => {
+  const options = {
+    ...DEFAULT_OPTS,
+    caller: getCaller({ name: 'metro', engine: 'hermes', platform: 'web', isDev: false }),
+  };
+
+  const sourceCode = `  
+    if (Platform.OS === 'ios') {
+      console.log('ios')
+    }
+    
+    Platform.select({
+      ios: () => console.log('ios'),
+      web: () => console.log('web'),
+      android: () => console.log('android'),
+    })
+    `;
+
+  expect(stripReactNativeImport(babel.transform(sourceCode, options)!.code!)).toEqual(
+    `(function(){return console.log('web');});`
+  );
+});
+it(`supports Platform module default fallback on web`, () => {
+  const options = {
+    ...DEFAULT_OPTS,
+    caller: getCaller({ name: 'metro', engine: 'hermes', platform: 'web', isDev: false }),
+  };
+
+  const sourceCode = `      
+    Platform.select({
+      ios: () => console.log('ios'),
+      default: () => console.log('default'),
+    })`;
+
+  expect(stripReactNativeImport(babel.transform(sourceCode, options)!.code!)).toEqual(
+    `(function(){return console.log('default');});`
+  );
+});
+
+xit(`removes Platform module and native fallback on web`, () => {
+  const options = {
+    ...DEFAULT_OPTS,
+    caller: getCaller({ name: 'metro', engine: 'hermes', platform: 'web', isDev: false }),
+  };
+
+  const sourceCode = `      
+    Platform.select({
+      native: () => console.log('native'),
+      default: () => console.log('default'),
+    })`;
+
+  expect(stripReactNativeImport(babel.transform(sourceCode, options)!.code!)).toEqual(
+    `(function(){return console.log('web');});`
+  );
+});
+
 it(`removes Platform module usage on web`, () => {
   const options = {
     ...DEFAULT_OPTS,