diff --git a/src/auth/googleauth.ts b/src/auth/googleauth.ts
index 65d288ed..5a3fb94f 100644
--- a/src/auth/googleauth.ts
+++ b/src/auth/googleauth.ts
@@ -379,42 +379,22 @@ export class GoogleAuth {
   /**
    * Create a credentials instance using the given input options.
    * @param {object=} json The input object.
-   * @param {function=} callback Optional callback.
-   * @returns Promise that resolves with the OAuth2Client (if no callback is
-   * passed)
+   * @returns JWT or UserRefresh Client with data
    */
-  // TODO: Remove the overloads and just keep this a sync API
-  fromJSON(json: JWTInput): JWT|UserRefreshClient;
-  fromJSON(json: JWTInput, callback: CredentialCallback): void;
-  fromJSON(json: JWTInput, callback?: CredentialCallback): JWT|UserRefreshClient
-      |void {
+  fromJSON(json: JWTInput): JWT|UserRefreshClient {
     let client: UserRefreshClient|JWT;
-    try {
-      if (!json) {
-        throw new Error(
-            'Must pass in a JSON object containing the Google auth settings.');
-      }
-
-      this.jsonContent = json;
-      if (json.type === 'authorized_user') {
-        client = new UserRefreshClient();
-      } else {
-        client = new JWT();
-      }
-      client.fromJSON(json);
-      if (callback) {
-        return callback(null, client);
-      } else {
-        return client;
-      }
-
-    } catch (e) {
-      if (callback) {
-        return callback(e);
-      } else {
-        throw e;
-      }
+    if (!json) {
+      throw new Error(
+          'Must pass in a JSON object containing the Google auth settings.');
+    }
+    this.jsonContent = json;
+    if (json.type === 'authorized_user') {
+      client = new UserRefreshClient();
+    } else {
+      client = new JWT();
     }
+    client.fromJSON(json);
+    return client;
   }
 
   /**
@@ -462,26 +442,12 @@ export class GoogleAuth {
   /**
    * Create a credentials instance using the given API key string.
    * @param {string} - The API key string
-   * @param {function=} - Optional callback function
+   * @returns A JWT loaded from the key
    */
-  fromAPIKey(
-      apiKey: string,
-      callback?: (err?: Error|null, client?: JWT) => void): void|JWT {
+  fromAPIKey(apiKey: string): JWT {
     const client = new JWT();
-    try {
-      client.fromAPIKey(apiKey);
-      if (callback) {
-        callback(null, client);
-      } else {
-        return client;
-      }
-    } catch (e) {
-      if (callback) {
-        callback(e);
-      } else {
-        throw e;
-      }
-    }
+    client.fromAPIKey(apiKey);
+    return client;
   }
 
   /**
diff --git a/src/auth/jwtaccess.ts b/src/auth/jwtaccess.ts
index 07cd7324..755a2ed1 100644
--- a/src/auth/jwtaccess.ts
+++ b/src/auth/jwtaccess.ts
@@ -57,74 +57,47 @@ export class JWTAccess {
    * @param {function} metadataCb a callback invoked with the jwt request metadata.
    * @returns a Promise that resolves with the request metadata response
    */
-  getRequestMetadata(authURI: string): RequestMetadataResponse;
-  getRequestMetadata(authURI: string, callback: RequestMetadataCallback): void;
-  getRequestMetadata(authURI: string, callback?: RequestMetadataCallback):
-      void|RequestMetadataResponse {
-    try {
-      const iat = Math.floor(new Date().getTime() / 1000);
-      const exp = iat + 3600;  // 3600 seconds = 1 hour
+  getRequestMetadata(authURI: string): RequestMetadataResponse {
+    const iat = Math.floor(new Date().getTime() / 1000);
+    const exp = iat + 3600;  // 3600 seconds = 1 hour
 
-      // The payload used for signed JWT headers has:
-      // iss == sub == <client email>
-      // aud == <the authorization uri>
-      const payload =
-          {iss: this.email, sub: this.email, aud: authURI, exp, iat};
-      const assertion = {
-        header: {alg: 'RS256'} as jws.Header,
-        payload,
-        secret: this.key
-      };
+    // The payload used for signed JWT headers has:
+    // iss == sub == <client email>
+    // aud == <the authorization uri>
+    const payload = {iss: this.email, sub: this.email, aud: authURI, exp, iat};
+    const assertion = {
+      header: {alg: 'RS256'} as jws.Header,
+      payload,
+      secret: this.key
+    };
 
-      // Sign the jwt and invoke metadataCb with it.
-      const signedJWT =
-          jws.sign({header: {alg: 'RS256'}, payload, secret: this.key});
-      const result = {
-        res: null,
-        headers: {Authorization: 'Bearer ' + signedJWT}
-      };
-      if (callback) {
-        callback(null, result.headers, null);
-      } else {
-        return result;
-      }
-    } catch (e) {
-      if (callback) {
-        callback(e);
-      } else {
-        throw e;
-      }
-    }
+    // Sign the jwt and invoke metadataCb with it.
+    const signedJWT =
+        jws.sign({header: {alg: 'RS256'}, payload, secret: this.key});
+    return {headers: {Authorization: 'Bearer ' + signedJWT}};
   }
 
   /**
    * Create a JWTAccess credentials instance using the given input options.
    * @param {object=} json The input object.
-   * @param {function=} callback Optional callback.
    */
-  fromJSON(json: JWTInput, callback?: (err: Error|null) => void) {
-    try {
-      if (!json) {
-        throw new Error(
-            'Must pass in a JSON object containing the service account auth settings.');
-      }
-      if (!json.client_email) {
-        throw new Error(
-            'The incoming JSON object does not contain a client_email field');
-      }
-      if (!json.private_key) {
-        throw new Error(
-            'The incoming JSON object does not contain a private_key field');
-      }
-      // Extract the relevant information from the json key file.
-      this.email = json.client_email;
-      this.key = json.private_key;
-      this.projectId = json.project_id;
-      if (callback) callback(null);
-    } catch (e) {
-      if (callback) return callback(e);
-      throw e;
+  fromJSON(json: JWTInput): void {
+    if (!json) {
+      throw new Error(
+          'Must pass in a JSON object containing the service account auth settings.');
+    }
+    if (!json.client_email) {
+      throw new Error(
+          'The incoming JSON object does not contain a client_email field');
+    }
+    if (!json.private_key) {
+      throw new Error(
+          'The incoming JSON object does not contain a private_key field');
     }
+    // Extract the relevant information from the json key file.
+    this.email = json.client_email;
+    this.key = json.private_key;
+    this.projectId = json.project_id;
   }
 
   /**
diff --git a/src/auth/jwtclient.ts b/src/auth/jwtclient.ts
index 07a11864..47241f36 100644
--- a/src/auth/jwtclient.ts
+++ b/src/auth/jwtclient.ts
@@ -147,34 +147,24 @@ export class JWT extends OAuth2Client {
   /**
    * Create a JWT credentials instance using the given input options.
    * @param {object=} json The input object.
-   * @param {function=} callback Optional callback.
    */
-  fromJSON(json: JWTInput, callback?: (err?: Error) => void): void {
-    try {
-      if (!json) {
-        throw new Error(
-            'Must pass in a JSON object containing the service account auth settings.');
-      }
-      if (!json.client_email) {
-        throw new Error(
-            'The incoming JSON object does not contain a client_email field');
-      }
-      if (!json.private_key) {
-        throw new Error(
-            'The incoming JSON object does not contain a private_key field');
-      }
-      // Extract the relevant information from the json key file.
-      this.email = json.client_email;
-      this.key = json.private_key;
-      this.projectId = json.project_id;
-    } catch (e) {
-      if (callback) {
-        callback(e);
-      } else {
-        throw e;
-      }
+  fromJSON(json: JWTInput): void {
+    if (!json) {
+      throw new Error(
+          'Must pass in a JSON object containing the service account auth settings.');
+    }
+    if (!json.client_email) {
+      throw new Error(
+          'The incoming JSON object does not contain a client_email field');
+    }
+    if (!json.private_key) {
+      throw new Error(
+          'The incoming JSON object does not contain a private_key field');
     }
-    if (callback) callback();
+    // Extract the relevant information from the json key file.
+    this.email = json.client_email;
+    this.key = json.private_key;
+    this.projectId = json.project_id;
   }
 
   /**
@@ -221,22 +211,12 @@ export class JWT extends OAuth2Client {
   /**
    * Creates a JWT credentials instance using an API Key for authentication.
    * @param {string} apiKey - the API Key in string form.
-   * @param {function=} callback - Optional callback to be invoked after
-   *  initialization.
    */
-  fromAPIKey(apiKey: string, callback?: (err?: Error) => void): void {
+  fromAPIKey(apiKey: string): void {
     if (!isString(apiKey)) {
-      const e = new Error('Must provide an API Key string.');
-      if (callback) {
-        return setImmediate(callback, e);
-      } else {
-        throw e;
-      }
+      throw new Error('Must provide an API Key string.');
     }
     this.apiKey = apiKey;
-    if (callback) {
-      return callback();
-    }
   }
 
   /**
diff --git a/src/auth/refreshclient.ts b/src/auth/refreshclient.ts
index 7e699cd5..75c38663 100644
--- a/src/auth/refreshclient.ts
+++ b/src/auth/refreshclient.ts
@@ -52,42 +52,32 @@ export class UserRefreshClient extends OAuth2Client {
    * Create a UserRefreshClient credentials instance using the given input
    * options.
    * @param {object=} json The input object.
-   * @param {function=} callback Optional callback.
    */
-  fromJSON(json: JWTInput, callback?: (err?: Error) => void) {
-    try {
-      if (!json) {
-        throw new Error(
-            'Must pass in a JSON object containing the user refresh token');
-      }
-      if (json.type !== 'authorized_user') {
-        throw new Error(
-            'The incoming JSON object does not have the "authorized_user" type');
-      }
-      if (!json.client_id) {
-        throw new Error(
-            'The incoming JSON object does not contain a client_id field');
-      }
-      if (!json.client_secret) {
-        throw new Error(
-            'The incoming JSON object does not contain a client_secret field');
-      }
-      if (!json.refresh_token) {
-        throw new Error(
-            'The incoming JSON object does not contain a refresh_token field');
-      }
-      this._clientId = json.client_id;
-      this._clientSecret = json.client_secret;
-      this._refreshToken = json.refresh_token;
-      this.credentials.refresh_token = json.refresh_token;
-    } catch (e) {
-      if (callback) {
-        callback(e);
-      } else {
-        throw e;
-      }
+  fromJSON(json: JWTInput): void {
+    if (!json) {
+      throw new Error(
+          'Must pass in a JSON object containing the user refresh token');
+    }
+    if (json.type !== 'authorized_user') {
+      throw new Error(
+          'The incoming JSON object does not have the "authorized_user" type');
+    }
+    if (!json.client_id) {
+      throw new Error(
+          'The incoming JSON object does not contain a client_id field');
+    }
+    if (!json.client_secret) {
+      throw new Error(
+          'The incoming JSON object does not contain a client_secret field');
+    }
+    if (!json.refresh_token) {
+      throw new Error(
+          'The incoming JSON object does not contain a refresh_token field');
     }
-    if (callback) callback();
+    this._clientId = json.client_id;
+    this._clientSecret = json.client_secret;
+    this._refreshToken = json.refresh_token;
+    this.credentials.refresh_token = json.refresh_token;
   }
 
   /**
diff --git a/test/test.googleauth.ts b/test/test.googleauth.ts
index 75b7cffe..eb83096f 100644
--- a/test/test.googleauth.ts
+++ b/test/test.googleauth.ts
@@ -158,13 +158,12 @@ function insertWellKnownFilePathIntoAuth(
 
 describe('GoogleAuth', () => {
   describe('.fromJson', () => {
-    it('should error on null json', (done) => {
+    it('should error on null json', () => {
       const auth = new GoogleAuth();
-      // Test verifies invalid parameter tests, which requires cast to any.
-      // tslint:disable-next-line no-any
-      (auth as any).fromJSON(null, (err: Error) => {
-        assert.equal(true, err instanceof Error);
-        done();
+      assert.throws(() => {
+        // Test verifies invalid parameter tests, which requires cast to any.
+        // tslint:disable-next-line no-any
+        (auth as any).fromJSON(null);
       });
     });
 
@@ -176,12 +175,12 @@ describe('GoogleAuth', () => {
         before(() => {
           auth = new GoogleAuth();
         });
-        it('Should error given an invalid api key', done => {
-          // Test verifies invalid parameter tests, which requires cast to any.
-          // tslint:disable-next-line no-any
-          (auth as any).fromAPIKey(null, (err: Error) => {
-            assert(err instanceof Error);
-            done();
+        it('Should error given an invalid api key', () => {
+          assert.throws(() => {
+            // Test verifies invalid parameter tests, which requires cast to
+            // any.
+            // tslint:disable-next-line no-any
+            (auth as any).fromAPIKey(null);
           });
         });
       });
@@ -212,23 +211,19 @@ describe('GoogleAuth', () => {
                       return [200, RESPONSE_BODY];
                     });
 
-            auth.fromAPIKey(API_KEY, (err, client) => {
-              assert.strictEqual(err, null);
-              if (client) {
-                client.request(
-                    {
-                      url: BASE_URL + ENDPOINT,
-                      method: 'POST',
-                      data: {'test': true}
-                    },
-                    (err2, res) => {
-                      assert.strictEqual(err2, null);
-                      assert.strictEqual(RESPONSE_BODY, res!.data);
-                      fakeService.done();
-                      done();
-                    });
-              }
-            });
+            const client = auth.fromAPIKey(API_KEY);
+            client.request(
+                {
+                  url: BASE_URL + ENDPOINT,
+                  method: 'POST',
+                  data: {'test': true}
+                },
+                (err2, res) => {
+                  assert.strictEqual(err2, null);
+                  assert.strictEqual(RESPONSE_BODY, res!.data);
+                  fakeService.done();
+                  done();
+                });
           });
         });
 
@@ -247,153 +242,128 @@ describe('GoogleAuth', () => {
                              uri.indexOf('test=' + OTHER_QS_PARAM.test) > -1);
                          return [200, RESPONSE_BODY];
                        });
-               auth.fromAPIKey(API_KEY, (err, client) => {
-                 assert.strictEqual(err, null);
-                 if (client) {
-                   client.request(
-                       {
-                         url: BASE_URL + ENDPOINT,
-                         method: 'POST',
-                         data: {'test': true},
-                         params: OTHER_QS_PARAM
-                       },
-                       (err2, res) => {
-                         assert.strictEqual(err2, null);
-                         assert.strictEqual(RESPONSE_BODY, res!.data);
-                         fakeService.done();
-                         done();
-                       });
-                 }
-               });
+               const client = auth.fromAPIKey(API_KEY);
+               client.request(
+                   {
+                     url: BASE_URL + ENDPOINT,
+                     method: 'POST',
+                     data: {'test': true},
+                     params: OTHER_QS_PARAM
+                   },
+                   (err2, res) => {
+                     assert.strictEqual(err2, null);
+                     assert.strictEqual(RESPONSE_BODY, res!.data);
+                     fakeService.done();
+                     done();
+                   });
              });
         });
       });
     });
 
     describe('JWT token', () => {
-      it('should error on empty json', (done) => {
+      it('should error on empty json', () => {
         const auth = new GoogleAuth();
-        auth.fromJSON({}, (err) => {
-          assert.equal(true, err instanceof Error);
-          done();
+        assert.throws(() => {
+          auth.fromJSON({});
         });
       });
 
-      it('should error on missing client_email', (done) => {
+      it('should error on missing client_email', () => {
         const json = createJwtJSON();
         delete json.client_email;
 
         const auth = new GoogleAuth();
-        auth.fromJSON(json, (err) => {
-          assert.equal(true, err instanceof Error);
-          done();
+        assert.throws(() => {
+          auth.fromJSON(json);
         });
       });
 
-      it('should error on missing private_key', (done) => {
+      it('should error on missing private_key', () => {
         const json = createJwtJSON();
         delete json.private_key;
 
         const auth = new GoogleAuth();
-        auth.fromJSON(json, (err) => {
-          assert.equal(true, err instanceof Error);
-          done();
+        assert.throws(() => {
+          auth.fromJSON(json);
         });
       });
 
-      it('should create JWT with client_email', (done) => {
+      it('should create JWT with client_email', () => {
         const json = createJwtJSON();
         const auth = new GoogleAuth();
-        auth.fromJSON(json, (err, result) => {
-          assert.equal(null, err);
-          assert.equal(json.client_email, (result as JWT).email);
-          done();
-        });
+        const result = auth.fromJSON(json);
+        assert.equal(json.client_email, (result as JWT).email);
       });
 
-      it('should create JWT with private_key', (done) => {
+      it('should create JWT with private_key', () => {
         const json = createJwtJSON();
         const auth = new GoogleAuth();
-        auth.fromJSON(json, (err, result) => {
-          assert.equal(null, err);
-          assert.equal(json.private_key, (result as JWT).key);
-          done();
-        });
+        const result = auth.fromJSON(json);
+        assert.equal(json.private_key, (result as JWT).key);
       });
 
-      it('should create JWT with null scopes', (done) => {
+      it('should create JWT with null scopes', () => {
         const json = createJwtJSON();
         const auth = new GoogleAuth();
-        auth.fromJSON(json, (err, result) => {
-          assert.equal(null, err);
-          assert.equal(null, (result as JWT).scopes);
-          done();
-        });
+        const result = auth.fromJSON(json);
+        assert.equal(null, (result as JWT).scopes);
       });
 
-      it('should create JWT with null subject', (done) => {
+      it('should create JWT with null subject', () => {
         const json = createJwtJSON();
         const auth = new GoogleAuth();
-        auth.fromJSON(json, (err, result) => {
-          assert.equal(null, err);
-          assert.equal(null, (result as JWT).subject);
-          done();
-        });
+        const result = auth.fromJSON(json);
+        assert.equal(null, (result as JWT).subject);
       });
 
-      it('should create JWT with null keyFile', (done) => {
+      it('should create JWT with null keyFile', () => {
         const json = createJwtJSON();
         const auth = new GoogleAuth();
-        auth.fromJSON(json, (err, result) => {
-          assert.equal(null, err);
-          assert.equal(null, (result as JWT).keyFile);
-          done();
-        });
+        const result = auth.fromJSON(json);
+        assert.equal(null, (result as JWT).keyFile);
       });
     });
+
     describe('Refresh token', () => {
-      it('should error on empty json', (done) => {
+      it('should error on empty json', () => {
         const auth = new GoogleAuth();
         const jwt = new auth.JWT();
-        jwt.fromJSON({}, (err) => {
-          assert.equal(true, err instanceof Error);
-          done();
+        assert.throws(() => {
+          jwt.fromJSON({});
         });
       });
 
-      it('should error on missing client_id', (done) => {
+      it('should error on missing client_id', () => {
         const json = createRefreshJSON();
         delete json.client_id;
 
         const auth = new GoogleAuth();
         const jwt = new auth.JWT();
-        jwt.fromJSON(json, (err) => {
-          assert.equal(true, err instanceof Error);
-          done();
+        assert.throws(() => {
+          jwt.fromJSON(json);
         });
       });
 
-      it('should error on missing client_secret', (done) => {
+      it('should error on missing client_secret', () => {
         const json = createRefreshJSON();
         delete json.client_secret;
 
         const auth = new GoogleAuth();
         const jwt = new auth.JWT();
-        jwt.fromJSON(json, (err) => {
-          assert.equal(true, err instanceof Error);
-          done();
+        assert.throws(() => {
+          jwt.fromJSON(json);
         });
       });
 
-      it('should error on missing refresh_token', done => {
+      it('should error on missing refresh_token', () => {
         const json = createRefreshJSON();
         delete json.refresh_token;
 
         const auth = new GoogleAuth();
         const jwt = new auth.JWT();
-        jwt.fromJSON(json, (err) => {
-          assert.equal(true, err instanceof Error);
-          done();
+        assert.throws(() => {
+          jwt.fromJSON(json);
         });
       });
     });
diff --git a/test/test.jwt.ts b/test/test.jwt.ts
index 09b17dbd..db519d43 100644
--- a/test/test.jwt.ts
+++ b/test/test.jwt.ts
@@ -456,78 +456,57 @@ describe('.fromJson', () => {
     jwt = new auth.JWT();
   });
 
-  it('should error on null json', (done) => {
-    // Test verifies invalid parameter tests, which requires cast to any.
-    // tslint:disable-next-line no-any
-    (jwt as any).fromJSON(null, (err: Error) => {
-      assert.equal(true, err instanceof Error);
-      done();
+  it('should error on null json', () => {
+    assert.throws(() => {
+      // Test verifies invalid parameter tests, which requires cast to any.
+      // tslint:disable-next-line no-any
+      (jwt as any).fromJSON(null);
     });
   });
 
-  it('should error on empty json', (done) => {
-    jwt.fromJSON({}, (err) => {
-      assert.equal(true, err instanceof Error);
-      done();
+  it('should error on empty json', () => {
+    assert.throws(() => {
+      jwt.fromJSON({});
     });
   });
 
-  it('should error on missing client_email', (done) => {
+  it('should error on missing client_email', () => {
     delete json.client_email;
-
-    jwt.fromJSON(json, (err) => {
-      assert.equal(true, err instanceof Error);
-      done();
+    assert.throws(() => {
+      jwt.fromJSON(json);
     });
   });
 
-  it('should error on missing private_key', (done) => {
+  it('should error on missing private_key', () => {
     delete json.private_key;
-
-    jwt.fromJSON(json, (err) => {
-      assert.equal(true, err instanceof Error);
-      done();
+    assert.throws(() => {
+      jwt.fromJSON(json);
     });
   });
 
-  it('should create JWT with client_email', (done) => {
-    jwt.fromJSON(json, (err) => {
-      assert.equal(null, err);
-      assert.equal(json.client_email, jwt.email);
-      done();
-    });
+  it('should create JWT with client_email', () => {
+    const result = jwt.fromJSON(json);
+    assert.equal(json.client_email, jwt.email);
   });
 
-  it('should create JWT with private_key', (done) => {
-    jwt.fromJSON(json, (err) => {
-      assert.equal(null, err);
-      assert.equal(json.private_key, jwt.key);
-      done();
-    });
+  it('should create JWT with private_key', () => {
+    const result = jwt.fromJSON(json);
+    assert.equal(json.private_key, jwt.key);
   });
 
-  it('should create JWT with null scopes', (done) => {
-    jwt.fromJSON(json, (err) => {
-      assert.equal(null, err);
-      assert.equal(null, jwt.scopes);
-      done();
-    });
+  it('should create JWT with null scopes', () => {
+    const result = jwt.fromJSON(json);
+    assert.equal(null, jwt.scopes);
   });
 
-  it('should create JWT with null subject', (done) => {
-    jwt.fromJSON(json, (err) => {
-      assert.equal(null, err);
-      assert.equal(null, jwt.subject);
-      done();
-    });
+  it('should create JWT with null subject', () => {
+    const result = jwt.fromJSON(json);
+    assert.equal(null, jwt.subject);
   });
 
-  it('should create JWT with null keyFile', (done) => {
-    jwt.fromJSON(json, (err) => {
-      assert.equal(null, err);
-      assert.equal(null, jwt.keyFile);
-      done();
-    });
+  it('should create JWT with null keyFile', () => {
+    const result = jwt.fromJSON(json);
+    assert.equal(null, jwt.keyFile);
   });
 });
 
@@ -581,31 +560,26 @@ describe('.fromAPIKey', () => {
     jwt = new auth.JWT();
   });
   describe('exception behaviour', () => {
-    it('should error without api key', (done) => {
-      // Test verifies invalid parameter tests, which requires cast to any.
-      // tslint:disable-next-line no-any
-      (jwt as any).fromAPIKey(undefined, (err: Error) => {
-        assert(err instanceof Error);
-        done();
+    it('should error without api key', () => {
+      assert.throws(() => {
+        // Test verifies invalid parameter tests, which requires cast to any.
+        // tslint:disable-next-line no-any
+        (jwt as any).fromAPIKey(undefined);
       });
     });
-    it('should error with invalid api key type', (done) => {
-      // Test verifies invalid parameter tests, which requires cast to any.
-      // tslint:disable-next-line no-any
-      jwt.fromAPIKey(({key: KEY} as any), (err) => {
-        assert(err instanceof Error);
-        done();
+    it('should error with invalid api key type', () => {
+      assert.throws(() => {
+        // Test verifies invalid parameter tests, which requires cast to any.
+        // tslint:disable-next-line no-any
+        jwt.fromAPIKey({key: KEY} as any);
       });
     });
   });
 
   describe('Valid behaviour', () => {
-    it('should set the .apiKey property on the instance', (done) => {
-      jwt.fromAPIKey(KEY, (err) => {
-        assert.strictEqual(jwt.apiKey, KEY);
-        assert.equal(err, null);
-        done();
-      });
+    it('should set the .apiKey property on the instance', () => {
+      const result = jwt.fromAPIKey(KEY);
+      assert.strictEqual(jwt.apiKey, KEY);
     });
   });
 });
diff --git a/test/test.jwtaccess.ts b/test/test.jwtaccess.ts
index c2bab1ce..437d7e14 100644
--- a/test/test.jwtaccess.ts
+++ b/test/test.jwtaccess.ts
@@ -37,30 +37,21 @@ function createJSON() {
 }
 
 describe('.getRequestMetadata', () => {
-  it('create a signed JWT token as the access token', (done) => {
+  it('create a signed JWT token as the access token', () => {
     const keys = keypair(1024 /* bitsize of private key */);
     const testUri = 'http:/example.com/my_test_service';
     const email = 'foo@serviceaccount.com';
     const auth = new GoogleAuth();
     const client = new auth.JWTAccess(email, keys.private);
-
-    const retValue = 'dummy';
-    const expectAuth =
-        (err: Error|null, headers?: http.IncomingHttpHeaders|null) => {
-          assert.strictEqual(null, err, 'no error was expected: got\n' + err);
-          assert.notStrictEqual(
-              null, headers, 'an creds object should be present');
-          const decoded = jws.decode(
-              (headers!.Authorization as string).replace('Bearer ', ''));
-          const payload = JSON.parse(decoded.payload);
-          assert.strictEqual(email, payload.iss);
-          assert.strictEqual(email, payload.sub);
-          assert.strictEqual(testUri, payload.aud);
-          done();
-          return retValue;
-        };
-    const res = client.getRequestMetadata(testUri, expectAuth);
-    assert.strictEqual(res, retValue);
+    const res = client.getRequestMetadata(testUri);
+    assert.notStrictEqual(
+        null, res.headers, 'an creds object should be present');
+    const decoded = jws.decode(
+        (res.headers!.Authorization as string).replace('Bearer ', ''));
+    const payload = JSON.parse(decoded.payload);
+    assert.strictEqual(email, payload.iss);
+    assert.strictEqual(email, payload.sub);
+    assert.strictEqual(testUri, payload.aud);
   });
 });
 
@@ -82,54 +73,42 @@ describe('.fromJson', () => {
     client = new auth.JWTAccess();
   });
 
-  it('should error on null json', (done) => {
-    // Test verifies invalid parameter tests, which requires cast to any.
-    // tslint:disable-next-line no-any
-    (client as any).fromJSON(null, (err: Error) => {
-      assert.equal(true, err instanceof Error);
-      done();
+  it('should error on null json', () => {
+    assert.throws(() => {
+      // Test verifies invalid parameter tests, which requires cast to any.
+      // tslint:disable-next-line no-any
+      (client as any).fromJSON(null);
     });
   });
 
-  it('should error on empty json', (done) => {
-    client.fromJSON({}, (err) => {
-      assert.equal(true, err instanceof Error);
-      done();
+  it('should error on empty json', () => {
+    assert.throws(() => {
+      client.fromJSON({});
     });
   });
 
-  it('should error on missing client_email', (done) => {
+  it('should error on missing client_email', () => {
     delete json.client_email;
-
-    client.fromJSON(json, (err) => {
-      assert.equal(true, err instanceof Error);
-      done();
+    assert.throws(() => {
+      client.fromJSON(json);
     });
   });
 
-  it('should error on missing private_key', (done) => {
+  it('should error on missing private_key', () => {
     delete json.private_key;
-
-    client.fromJSON(json, (err) => {
-      assert.equal(true, err instanceof Error);
-      done();
+    assert.throws(() => {
+      client.fromJSON(json);
     });
   });
 
-  it('should create JWT with client_email', (done) => {
-    client.fromJSON(json, (err) => {
-      assert.equal(null, err);
-      assert.equal(json.client_email, client.email);
-      done();
-    });
+  it('should create JWT with client_email', () => {
+    const result = client.fromJSON(json);
+    assert.equal(json.client_email, client.email);
   });
 
-  it('should create JWT with private_key', (done) => {
-    client.fromJSON(json, (err) => {
-      assert.equal(null, err);
-      assert.equal(json.private_key, client.key);
-      done();
-    });
+  it('should create JWT with private_key', () => {
+    const result = client.fromJSON(json);
+    assert.equal(json.private_key, client.key);
   });
 });
 
diff --git a/test/test.refresh.ts b/test/test.refresh.ts
index 778b9a57..aed9cb63 100644
--- a/test/test.refresh.ts
+++ b/test/test.refresh.ts
@@ -33,95 +33,78 @@ function createJSON() {
 }
 
 describe('.fromJson', () => {
-  it('should error on null json', (done) => {
+  it('should error on null json', () => {
     const auth = new GoogleAuth();
     const refresh = new auth.UserRefreshClient();
-    // Test verifies invalid parameter tests, which requires cast to any.
-    // tslint:disable-next-line no-any
-    (refresh as any).fromJSON(null, (err: Error) => {
-      assert.equal(true, err instanceof Error);
-      done();
+    assert.throws(() => {
+      // Test verifies invalid parameter tests, which requires cast to any.
+      // tslint:disable-next-line no-any
+      (refresh as any).fromJSON(null);
     });
   });
 
-  it('should error on empty json', (done) => {
+  it('should error on empty json', () => {
     const auth = new GoogleAuth();
     const refresh = new auth.UserRefreshClient();
-    // Test verifies invalid parameter tests, which requires cast to any.
-    // tslint:disable-next-line no-any
-    refresh.fromJSON(({} as any), (err) => {
-      assert.equal(true, err instanceof Error);
-      done();
+    assert.throws(() => {
+      // Test verifies invalid parameter tests, which requires cast to any.
+      // tslint:disable-next-line no-any
+      refresh.fromJSON({});
     });
   });
 
-  it('should error on missing client_id', (done) => {
+  it('should error on missing client_id', () => {
     const json = createJSON();
     delete json.client_id;
-
     const auth = new GoogleAuth();
     const refresh = new auth.UserRefreshClient();
-    refresh.fromJSON(json, (err) => {
-      assert.equal(true, err instanceof Error);
-      done();
+    assert.throws(() => {
+      refresh.fromJSON(json);
     });
   });
 
-  it('should error on missing client_secret', (done) => {
+  it('should error on missing client_secret', () => {
     const json = createJSON();
     delete json.client_secret;
-
     const auth = new GoogleAuth();
     const refresh = new auth.UserRefreshClient();
-    refresh.fromJSON(json, (err) => {
-      assert.equal(true, err instanceof Error);
-      done();
+    assert.throws(() => {
+      refresh.fromJSON(json);
     });
   });
 
-  it('should error on missing refresh_token', (done) => {
+  it('should error on missing refresh_token', () => {
     const json = createJSON();
     delete json.refresh_token;
-
     const auth = new GoogleAuth();
     const refresh = new auth.UserRefreshClient();
-    refresh.fromJSON(json, (err) => {
-      assert.equal(true, err instanceof Error);
-      done();
+    assert.throws(() => {
+      refresh.fromJSON(json);
     });
   });
 
-  it('should create UserRefreshClient with clientId_', (done) => {
+  it('should create UserRefreshClient with clientId_', () => {
     const json = createJSON();
     const auth = new GoogleAuth();
     const refresh = new auth.UserRefreshClient();
-    refresh.fromJSON(json, (err) => {
-      assert.ifError(err);
-      assert.equal(json.client_id, refresh._clientId);
-      done();
-    });
+    const result = refresh.fromJSON(json);
+    assert.equal(json.client_id, refresh._clientId);
   });
 
-  it('should create UserRefreshClient with clientSecret_', (done) => {
+  it('should create UserRefreshClient with clientSecret_', () => {
     const json = createJSON();
     const auth = new GoogleAuth();
     const refresh = new auth.UserRefreshClient();
-    refresh.fromJSON(json, (err) => {
-      assert.ifError(err);
-      assert.equal(json.client_secret, refresh._clientSecret);
-      done();
-    });
+    const result = refresh.fromJSON(json);
+    assert.equal(json.client_secret, refresh._clientSecret);
   });
 
-  it('should create UserRefreshClient with _refreshToken', (done) => {
+  it('should create UserRefreshClient with _refreshToken', () => {
     const json = createJSON();
     const auth = new GoogleAuth();
     const refresh = new auth.UserRefreshClient();
-    refresh.fromJSON(json, (err) => {
-      assert.ifError(err);
-      assert.equal(json.refresh_token, refresh._refreshToken);
-      done();
-    });
+    const result = refresh.fromJSON(json);
+    assert.equal(json.refresh_token, refresh._refreshToken);
   });
 });