diff --git a/.circleci/config.yml b/.circleci/config.yml
index 80224a400..c375c056b 100644
--- a/.circleci/config.yml
+++ b/.circleci/config.yml
@@ -45,25 +45,36 @@ jobs:
             npm install
             npm test
       - run:
-          name: Run unit tests of the generated Showcase library
+          name: Run unit tests and gts fix of the generated Showcase library
           command: |
             cd .test-out-showcase
             npm install
             npm test
+            npm run fix
       - run:
-          name: Run unit tests of the generated KMS library
+          name: Run unit tests and gts fix of the generated KMS library
           command: |
             cp -r typescript/test/protos ./.test-out-keymanager
             cd .test-out-keymanager
             npm install
             npm test
+            npm run fix
       - run:
-          name: Run unit tests of the generated Text-to-Speech library
+          name: Run unit tests and gts fix of the generated Translate library
+          command: |
+            cp -r typescript/test/protos ./.test-out-translate
+            cd .test-out-translate
+            npm install
+            npm test
+            npm run fix
+      - run:
+          name: Run unit tests and gts fix of the generated Text-to-Speech library
           command: |
             cp -r typescript/test/protos ./.test-out-texttospeech
             cd .test-out-texttospeech
             npm install
             npm test
+            npm run fix
       - run:
           name: Run linting
           command: |
diff --git a/templates/typescript_gapic/package.json.njk b/templates/typescript_gapic/package.json.njk
index 09f1f5f17..a4b02f555 100644
--- a/templates/typescript_gapic/package.json.njk
+++ b/templates/typescript_gapic/package.json.njk
@@ -13,6 +13,7 @@
     "google-gax": "^1.7.5"
   },
   "devDependencies": {
+    "@types/node": "^12.0.0",
     "@types/mocha": "^5.2.5",
     "gts": "^0.9.0",
     "mocha": "^6.0.0",
diff --git a/templates/typescript_gapic/test/gapic-$service-$version.ts.njk b/templates/typescript_gapic/test/gapic-$service-$version.ts.njk
index 5de1f16b8..cf91bc034 100644
--- a/templates/typescript_gapic/test/gapic-$service-$version.ts.njk
+++ b/templates/typescript_gapic/test/gapic-$service-$version.ts.njk
@@ -1,24 +1,27 @@
 {% import "../_license.njk" as license -%}
 {% import "../_util.njk" as util -%}
 {{license.license()}}
-'use strict';
 import * as protosTypes from '../protos/protos';
-const assert = require('assert');
+import * as assert from 'assert';
 const {{ service.name.toLowerCase() }}Module = require('../src');
 {% if (service.streaming.length > 0) %}
-const {PassThrough} = require('stream');
+import {PassThrough} from 'stream';
 {% endif %}
 
 const FAKE_STATUS_CODE = 1;
 class FakeError{
+    name: string;
+    message: string;
     code: number;
     constructor(n: number){
+        this.name = 'fakeName';
+        this.message = 'fake message';
         this.code = n;
     }
 }
 const error = new FakeError(FAKE_STATUS_CODE);
 export interface Callback {
-  (err: FakeError|null, response?: {} | null): {};
+  (err: FakeError|null, response?: {} | null): void;
 }
 
 export class Operation{
diff --git a/typescript/test/testdata/keymanager/package.json.baseline b/typescript/test/testdata/keymanager/package.json.baseline
index 7f4ff3296..31b1b661c 100644
--- a/typescript/test/testdata/keymanager/package.json.baseline
+++ b/typescript/test/testdata/keymanager/package.json.baseline
@@ -13,6 +13,7 @@
     "google-gax": "^1.7.5"
   },
   "devDependencies": {
+    "@types/node": "^12.0.0",
     "@types/mocha": "^5.2.5",
     "gts": "^0.9.0",
     "mocha": "^6.0.0",
diff --git a/typescript/test/testdata/keymanager/test/gapic-key_management_service-v1.ts.baseline b/typescript/test/testdata/keymanager/test/gapic-key_management_service-v1.ts.baseline
index 46299b643..1f51424e8 100644
--- a/typescript/test/testdata/keymanager/test/gapic-key_management_service-v1.ts.baseline
+++ b/typescript/test/testdata/keymanager/test/gapic-key_management_service-v1.ts.baseline
@@ -16,22 +16,25 @@
 // ** https://github.com/googleapis/gapic-generator-typescript **
 // ** All changes to this file may be overwritten. **
 
-'use strict';
 import * as protosTypes from '../protos/protos';
-const assert = require('assert');
+import * as assert from 'assert';
 const keymanagementserviceModule = require('../src');
 
 
 const FAKE_STATUS_CODE = 1;
 class FakeError{
+    name: string;
+    message: string;
     code: number;
     constructor(n: number){
+        this.name = 'fakeName';
+        this.message = 'fake message';
         this.code = n;
     }
 }
 const error = new FakeError(FAKE_STATUS_CODE);
 export interface Callback {
-  (err: FakeError|null, response?: {} | null): {};
+  (err: FakeError|null, response?: {} | null): void;
 }
 
 export class Operation{
diff --git a/typescript/test/testdata/showcase/package.json.baseline b/typescript/test/testdata/showcase/package.json.baseline
index 4d4f3c1ad..a0ec01deb 100644
--- a/typescript/test/testdata/showcase/package.json.baseline
+++ b/typescript/test/testdata/showcase/package.json.baseline
@@ -13,6 +13,7 @@
     "google-gax": "^1.7.5"
   },
   "devDependencies": {
+    "@types/node": "^12.0.0",
     "@types/mocha": "^5.2.5",
     "gts": "^0.9.0",
     "mocha": "^6.0.0",
diff --git a/typescript/test/testdata/showcase/test/gapic-echo-v1beta1.ts.baseline b/typescript/test/testdata/showcase/test/gapic-echo-v1beta1.ts.baseline
index 704e42eb2..90e1a9d3e 100644
--- a/typescript/test/testdata/showcase/test/gapic-echo-v1beta1.ts.baseline
+++ b/typescript/test/testdata/showcase/test/gapic-echo-v1beta1.ts.baseline
@@ -16,24 +16,27 @@
 // ** https://github.com/googleapis/gapic-generator-typescript **
 // ** All changes to this file may be overwritten. **
 
-'use strict';
 import * as protosTypes from '../protos/protos';
-const assert = require('assert');
+import * as assert from 'assert';
 const echoModule = require('../src');
 
-const {PassThrough} = require('stream');
+import {PassThrough} from 'stream';
 
 
 const FAKE_STATUS_CODE = 1;
 class FakeError{
+    name: string;
+    message: string;
     code: number;
     constructor(n: number){
+        this.name = 'fakeName';
+        this.message = 'fake message';
         this.code = n;
     }
 }
 const error = new FakeError(FAKE_STATUS_CODE);
 export interface Callback {
-  (err: FakeError|null, response?: {} | null): {};
+  (err: FakeError|null, response?: {} | null): void;
 }
 
 export class Operation{
diff --git a/typescript/test/testdata/texttospeech/package.json.baseline b/typescript/test/testdata/texttospeech/package.json.baseline
index f472103bd..3e81b973d 100644
--- a/typescript/test/testdata/texttospeech/package.json.baseline
+++ b/typescript/test/testdata/texttospeech/package.json.baseline
@@ -13,6 +13,7 @@
     "google-gax": "^1.7.5"
   },
   "devDependencies": {
+    "@types/node": "^12.0.0",
     "@types/mocha": "^5.2.5",
     "gts": "^0.9.0",
     "mocha": "^6.0.0",
diff --git a/typescript/test/testdata/texttospeech/test/gapic-text_to_speech-v1.ts.baseline b/typescript/test/testdata/texttospeech/test/gapic-text_to_speech-v1.ts.baseline
index bcf655cf1..622773d20 100644
--- a/typescript/test/testdata/texttospeech/test/gapic-text_to_speech-v1.ts.baseline
+++ b/typescript/test/testdata/texttospeech/test/gapic-text_to_speech-v1.ts.baseline
@@ -16,22 +16,25 @@
 // ** https://github.com/googleapis/gapic-generator-typescript **
 // ** All changes to this file may be overwritten. **
 
-'use strict';
 import * as protosTypes from '../protos/protos';
-const assert = require('assert');
+import * as assert from 'assert';
 const texttospeechModule = require('../src');
 
 
 const FAKE_STATUS_CODE = 1;
 class FakeError{
+    name: string;
+    message: string;
     code: number;
     constructor(n: number){
+        this.name = 'fakeName';
+        this.message = 'fake message';
         this.code = n;
     }
 }
 const error = new FakeError(FAKE_STATUS_CODE);
 export interface Callback {
-  (err: FakeError|null, response?: {} | null): {};
+  (err: FakeError|null, response?: {} | null): void;
 }
 
 export class Operation{
diff --git a/typescript/test/testdata/translate/package.json.baseline b/typescript/test/testdata/translate/package.json.baseline
index 9b16c43d2..c1f43321a 100644
--- a/typescript/test/testdata/translate/package.json.baseline
+++ b/typescript/test/testdata/translate/package.json.baseline
@@ -13,6 +13,7 @@
     "google-gax": "^1.7.5"
   },
   "devDependencies": {
+    "@types/node": "^12.0.0",
     "@types/mocha": "^5.2.5",
     "gts": "^0.9.0",
     "mocha": "^6.0.0",
diff --git a/typescript/test/testdata/translate/test/gapic-translation_service-v3beta1.ts.baseline b/typescript/test/testdata/translate/test/gapic-translation_service-v3beta1.ts.baseline
index 23c4ec05f..33d9175d9 100644
--- a/typescript/test/testdata/translate/test/gapic-translation_service-v3beta1.ts.baseline
+++ b/typescript/test/testdata/translate/test/gapic-translation_service-v3beta1.ts.baseline
@@ -16,22 +16,25 @@
 // ** https://github.com/googleapis/gapic-generator-typescript **
 // ** All changes to this file may be overwritten. **
 
-'use strict';
 import * as protosTypes from '../protos/protos';
-const assert = require('assert');
+import * as assert from 'assert';
 const translationserviceModule = require('../src');
 
 
 const FAKE_STATUS_CODE = 1;
 class FakeError{
+    name: string;
+    message: string;
     code: number;
     constructor(n: number){
+        this.name = 'fakeName';
+        this.message = 'fake message';
         this.code = n;
     }
 }
 const error = new FakeError(FAKE_STATUS_CODE);
 export interface Callback {
-  (err: FakeError|null, response?: {} | null): {};
+  (err: FakeError|null, response?: {} | null): void;
 }
 
 export class Operation{