don't write imports to test helpers if they aren't actually used in the file after transformation

Author: fivetanley

transforms/integration/__testfixtures__/default-component-test.output.js

@@ -1,4 +1,3 @@
-import { find } from '@ember/test-helpers';
 import { moduleForComponent, test } from 'ember-qunit';
 import hbs from 'htmlbars-inline-precompile';
 

transforms/native-dom/__testfixtures__/context-argument.output.js

@@ -1,4 +1,4 @@
-import { find, findAll, visit, click, fillIn } from '@ember/test-helpers';
+import { find, findAll, visit, click } from '@ember/test-helpers';
 import { test } from 'qunit';
 import moduleForAcceptance from '../../tests/helpers/module-for-acceptance';
 

transforms/native-dom/__testfixtures__/double-import.input.js

@@ -1,2 +1,9 @@
 import { click, currentURL } from 'ember-native-dom-helpers';
 import { find, visit } from 'ember-native-dom-helpers';
+
+test('visiting /foo', async function(assert) {
+  await visit('/foo');
+  await click('.foo');
+  assert.ok(find('.foo'));
+  assert.ok(currentURL());
+});

transforms/native-dom/__testfixtures__/double-import.output.js

@@ -1 +1,8 @@
 import { click, currentURL, find, visit } from '@ember/test-helpers';
+
+test('visiting /foo', async function(assert) {
+  await visit('/foo');
+  await click('.foo');
+  assert.ok(find('.foo'));
+  assert.ok(currentURL());
+});

transforms/native-dom/__testfixtures__/prune-import.input.js

@@ -1 +1,3 @@
 import { click } from 'ember-native-dom-helpers';
+
+click('.foo');

transforms/native-dom/__testfixtures__/prune-import.output.js

@@ -1 +1,3 @@
 import { click } from '@ember/test-helpers';
+
+click('.foo');

transforms/utils.js

@@ -360,13 +360,25 @@ function writeImportStatements(j, root) {
       source: { value: '@ember/test-helpers' }
     });
 
+    let actuallyNeedsImport = Array.from(_statementsToImport).filter(methodName => {
+      return root.find(j.CallExpression, {
+        callee: {
+          name: methodName
+        }
+      }).length > 0;
+    });
+
+    if (actuallyNeedsImport.length === 0) {
+      return;
+    }
+
     if (importStatement.length === 0) {
-      importStatement = createImportStatement(j, '@ember/test-helpers', 'default', Array.from(_statementsToImport));
+      importStatement = createImportStatement(j, '@ember/test-helpers', 'default', actuallyNeedsImport);
       body.unshift(importStatement);
     } else {
       let existingSpecifiers = importStatement.get("specifiers");
 
-      _statementsToImport.forEach(name => {
+      actuallyNeedsImport.forEach(name => {
         if (existingSpecifiers.filter(exSp => exSp.value.imported.name === name).length === 0) {
           existingSpecifiers.push(j.importSpecifier(j.identifier(name)));
         }