Add a failing test for common chunk bug

This reproduces issue #365.

test-scenarios/common-chunk-test.ts

@@ -0,0 +1,101 @@
+import { appScenarios } from './scenarios';
+import { PreparedApp } from '@ef4/test-support';
+import QUnit from 'qunit';
+import merge from 'lodash/merge';
+const { module: Qmodule, test } = QUnit;
+
+appScenarios
+  .map('common-chunk', project => {
+    project.linkDevDependency('ember-auto-import', { baseDir: __dirname });
+
+    project.addDevDependency('some-lib', {
+      files: {
+        'left.js': `
+          import { helper } from './common';
+          export function left() {
+            return helper('left');
+          }
+        `,
+        'right.js': `
+          import { helper } from './common';
+          export function right() {
+            return helper('right');
+          }
+        `,
+        'common.js': `
+          export function helper(msg) {
+            return "the message is " + msg;
+          }
+        `,
+      },
+    });
+
+    merge(project.files, {
+      'ember-cli-build.js': `
+        const EmberApp = require('ember-cli/lib/broccoli/ember-app');
+        module.exports = function (defaults) {
+          let app = new EmberApp(defaults, {
+            babel: {
+              plugins: [
+                require('ember-auto-import/babel-plugin')
+              ],
+            },
+            autoImport: {
+              webpack: {
+                optimization: {
+                  splitChunks: {
+                    // for test purposes, we want chunk
+                    // splitting even though our common chunk is very small
+                    minSize: 0
+                  }
+                }
+              }
+            }
+          });
+          return app.toTree();
+        };
+      `,
+      app: {
+        lib: {
+          'example.js': `
+            export async function useLeft() {
+              let { left } = await import('some-lib/left');
+              return left();
+            }
+            export async function useRight() {
+              let { right } = await import('some-lib/right');
+              return right();
+            }
+          `,
+        },
+      },
+      tests: {
+        unit: {
+          'example-test.js': `
+            import { module, test } from 'qunit';
+            import { useLeft, useRight } from '@ef4/app-template/lib/example';
+
+            module('Unit | common chunk', function () {
+              test('can use two dynamic imports that share a common chunk', async function(assert) {
+                assert.equal(await useLeft(), 'The message is left');
+                assert.equal(await useRight(), 'The message is right');
+              });
+            });
+          `,
+        },
+      },
+    });
+  })
+  .forEachScenario(scenario => {
+    Qmodule(scenario.name, function (hooks) {
+      let app: PreparedApp;
+      hooks.before(async () => {
+        app = await scenario.prepare();
+      });
+
+      test('npm run test', async function (assert) {
+        let result = await app.execute('npm run test');
+        assert.equal(result.exitCode, 0, result.output);
+      });
+    });
+  });