explicitly test the interop patterns

test/es-module/test-require-as-esm-interop.js

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+// Flags: --experimental-require-module
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+
+// This test demonstrates interop between CJS and CJS represented as ESM
+// under the `__cjsModule` pattern.
+(async () => {
+  // dep.js and index.js are CJS modules.
+  // dep exports 'cjs', while index reexports dep:
+  assert.strictEqual(require('../fixtures/cjsesm/dep.js'), 'cjs');
+  assert.strictEqual(require('../fixtures/cjsesm/index.js'), 'cjs');
+
+  // Now we have ESM conversions of these dependencies, using __cjsModule, 
+  // that behave equivalently under require(esm) despite the custom string import:
+  assert.strictEqual(require('../fixtures/cjsesm/dep.mjs'), 'cjs');
+  assert.strictEqual(require('../fixtures/cjsesm/index.mjs'), 'cjs');
+
+  // Furthermore, if `index.mjs` imports from `dep.mjs` directly, the reexport
+  // still works:
+  assert.strictEqual(require('../fixtures/cjsesm/index-importing-depmjs.mjs'), 'cjs');
+
+  // Finally, the ESM representations under these conversions all match equivalently:
+  const esmCjsImport = await import('../fixtures/cjsesm/index.js');
+
+  assert.deepStrictEqual(await import('../fixtures/cjsesm/index.mjs'), esmCjsImport);
+  assert.deepStrictEqual(await import('../fixtures/cjsesm/index-importing-depmjs.mjs'), esmCjsImport);
+})().then(common.mustCall());

test/fixtures/cjsesm/dep.js

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+module.exports = 'cjs';

test/fixtures/cjsesm/dep.mjs

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+export default 'cjs';
+export const __cjsModule = true;

test/fixtures/cjsesm/index-importing-depmjs.mjs

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+import dep from './dep.mjs';
+export default dep;
+export const __cjsModule = true;

test/fixtures/cjsesm/index.js

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+const dep = require('./dep.js');
+module.exports = dep;

test/fixtures/cjsesm/index.mjs

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+import dep from './dep.js';
+export default dep;
+export const __cjsModule = true;