diff --git a/.travis.yml b/.travis.yml
index f4a1983..a32795a 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,11 +1,9 @@
 language: php
 dist: trusty
 php:
-    - 5.5
-    - 5.6
-    - 7.0
-    - 7.1
     - 7.2
+    - 7.3
+    - 7.4
 
 install:
     - composer install
diff --git a/composer.json b/composer.json
index 9a9ccab..f1ec58a 100644
--- a/composer.json
+++ b/composer.json
@@ -17,11 +17,11 @@
     ],
 
     "require": {
-        "php": "^5.5.9|^7.0.8|^7.1.3|^7.2.5",
-        "symfony/http-foundation": "~3.0|~4.0|~5.0"
+        "php": "^7.2",
+        "symfony/http-foundation": "^4.4|^5.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4.8 || ^5.0"
+        "phpunit/phpunit": "^8.5"
     },
 
     "autoload": {
diff --git a/lib/OAuth2.php b/lib/OAuth2.php
index 637372d..96753ee 100644
--- a/lib/OAuth2.php
+++ b/lib/OAuth2.php
@@ -2,7 +2,6 @@
 
 namespace OAuth2;
 
-use OAuth2\Model\IOAuth2AccessToken;
 use OAuth2\Model\IOAuth2AuthCode;
 use OAuth2\Model\IOAuth2Client;
 use Symfony\Component\HttpFoundation\Request;
@@ -1008,13 +1007,12 @@ protected function getClientCredentials(array $inputData, array $authHeaders)
      *
      * @throws OAuth2ServerException
      * @throws OAuth2RedirectException
-     *
      * @see     http://tools.ietf.org/html/draft-ietf-oauth-v2-20#section-4.1.1
      * @see     http://tools.ietf.org/html/draft-ietf-oauth-v2-21#section-10.12
      *
      * @ingroup oauth2_section_3
      */
-    protected function getAuthorizeParams(Request $request = null)
+    public function getAuthorizeParams(Request $request = null)
     {
         $filters = array(
             "client_id" => array(
diff --git a/phpunit.xml.dist b/phpunit.xml.dist
index c27823d..4d8da63 100644
--- a/phpunit.xml.dist
+++ b/phpunit.xml.dist
@@ -8,7 +8,6 @@
          convertWarningsToExceptions="true"
          processIsolation="false"
          stopOnFailure="false"
-         syntaxCheck="false"
          bootstrap="vendor/autoload.php"
 >
   <testsuites>
diff --git a/tests/ExtraHeadersTest.php b/tests/ExtraHeadersTest.php
index 52030d4..39a1f17 100644
--- a/tests/ExtraHeadersTest.php
+++ b/tests/ExtraHeadersTest.php
@@ -1,22 +1,25 @@
 <?php
 
+namespace OAuth2\Tests;
+
 use OAuth2\OAuth2;
 use OAuth2\Model\OAuth2Client;
+use PHPUnit\Framework\TestCase;
 use Symfony\Component\HttpFoundation\Request;
 use OAuth2\Tests\Fixtures\OAuth2GrantUserStub;
 
 /**
  * Extra Headers test case.
  */
-class ExtraHeadersTest extends PHPUnit_Framework_TestCase
+class ExtraHeadersTest extends TestCase
 {
-    public function testErrorResponseContainsExtraHeaders()
+    public function testErrorResponseContainsExtraHeaders(): void
     {
         $config = array(
-            OAuth2::CONFIG_RESPONSE_EXTRA_HEADERS => array(
-                "Access-Control-Allow-Origin" => "http://www.foo.com",
-                "X-Extra-Header-1" => "Foo-Bar",
-            ),
+            OAuth2::CONFIG_RESPONSE_EXTRA_HEADERS => [
+                'Access-Control-Allow-Origin' => 'http://www.foo.com',
+                'X-Extra-Header-1' => 'Foo-Bar',
+            ],
         );
         $stub = new OAuth2GrantUserStub();
         $stub->addClient(new OAuth2Client('cid', 'cpass'));
@@ -32,7 +35,7 @@ public function testErrorResponseContainsExtraHeaders()
             'username' => 'foo',
             'password' => 'bar',
         )));
-        $this->assertSame("http://www.foo.com", $response->headers->get("Access-Control-Allow-Origin"));
-        $this->assertSame("Foo-Bar", $response->headers->get("X-Extra-Header-1"));
+        $this->assertSame('http://www.foo.com', $response->headers->get('Access-Control-Allow-Origin'));
+        $this->assertSame('Foo-Bar', $response->headers->get('X-Extra-Header-1'));
     }
 }
diff --git a/tests/Model/OAuth2TokenTest.php b/tests/Model/OAuth2TokenTest.php
index 9f06064..508c4a1 100644
--- a/tests/Model/OAuth2TokenTest.php
+++ b/tests/Model/OAuth2TokenTest.php
@@ -3,10 +3,11 @@
 namespace OAuth2\Tests\Model;
 
 use OAuth2\Model\OAuth2Token;
+use PHPUnit\Framework\TestCase;
 
-class OAuth2TokenTest extends \PHPUnit_Framework_TestCase
+class OAuth2TokenTest extends TestCase
 {
-    public function testConstruct()
+    public function testConstruct(): void
     {
         $expiresAt = time() + 42;
         $data = new \stdClass;
@@ -23,14 +24,14 @@ public function testConstruct()
     }
 
     /** @dataProvider getTestExpiresData */
-    public function testExpires($offset, $expired)
+    public function testExpires($offset, $expired): void
     {
         $token = new OAuth2Token('foo', 'bar', time() + $offset);
 
         $this->assertSame($expired, $token->hasExpired());
     }
 
-    public function getTestExpiresData()
+    public function getTestExpiresData(): array
     {
         return array(
             array(-10, true),
diff --git a/tests/OAuth2ImplicitGrantTypeTest.php b/tests/OAuth2ImplicitGrantTypeTest.php
index 4eb6f22..8e4f7ef 100644
--- a/tests/OAuth2ImplicitGrantTypeTest.php
+++ b/tests/OAuth2ImplicitGrantTypeTest.php
@@ -1,21 +1,24 @@
 <?php
 
+namespace OAuth2\Tests;
+
 use OAuth2\OAuth2;
 use OAuth2\OAuth2ServerException;
 use OAuth2\Model\OAuth2Client;
 use OAuth2\Tests\Fixtures\OAuth2ImplicitStub;
+use PHPUnit\Framework\TestCase;
 use Symfony\Component\HttpFoundation\Request;
 
 /**
  * OAuth2 test case.
  */
-class OAuth2ImplicitGrantTypeTest extends PHPUnit_Framework_TestCase
+class OAuth2ImplicitGrantTypeTest extends TestCase
 {
     /**
      * Tests OAuth2->grantAccessToken() with implicit
      *
      */
-    public function testGrantAccessTokenWithGrantImplicit()
+    public function testGrantAccessTokenWithGrantImplicit(): void
     {
         $stub = new OAuth2ImplicitStub();
         $stub->addClient(new OAuth2Client('blah', 'foo', array('http://www.example.com/')));
@@ -37,7 +40,7 @@ public function testGrantAccessTokenWithGrantImplicit()
      * Tests OAuth2->grantAccessToken() with implicit
      *
      */
-    public function testRejectedAccessTokenWithGrantImplicit()
+    public function testRejectedAccessTokenWithGrantImplicit(): void
     {
         //$this->fixture->grantAccessToken(/* parameters */);
 
@@ -58,9 +61,9 @@ public function testRejectedAccessTokenWithGrantImplicit()
         } catch (OAuth2ServerException $e) {
             $this->assertSame('access_denied', $e->getMessage());
             $this->assertSame('The user denied access to your application', $e->getDescription());
-            $this->assertSame(array(
+            $this->assertSame([
                 'Location' => 'http://www.example.com/?foo=bar#error=access_denied&error_description=The+user+denied+access+to+your+application&state=42',
-            ), $e->getResponseHeaders());
+            ], $e->getResponseHeaders());
         }
     }
 }
diff --git a/tests/OAuth2OutputTest.php b/tests/OAuth2OutputTest.php
index 1db2331..9407bdf 100644
--- a/tests/OAuth2OutputTest.php
+++ b/tests/OAuth2OutputTest.php
@@ -1,14 +1,19 @@
 <?php
 
+namespace OAuth2\Tests;
+
 use OAuth2\OAuth2;
 use OAuth2\Model\OAuth2AuthCode;
 use OAuth2\Model\OAuth2Client;
+use PHPUnit\Framework\MockObject\MockObject;
+use PHPUnit\Framework\TestCase;
 use Symfony\Component\HttpFoundation\Request;
+use OAuth2\IOAuth2GrantCode;
 
 /**
  * OAuth2 test cases that involve capturing output.
  */
-class OAuth2OutputTest extends PHPUnit_Framework_TestCase
+class OAuth2OutputTest extends TestCase
 {
     /**
      * @var OAuth2
@@ -19,17 +24,23 @@ class OAuth2OutputTest extends PHPUnit_Framework_TestCase
      * Tests OAuth2->grantAccessToken() with successful Auth code grant
      *
      */
-    public function testGrantAccessTokenWithGrantAuthCodeSuccess()
+    public function testGrantAccessTokenWithGrantAuthCodeSuccess(): void
     {
         $request = new Request(
-            array('grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE, 'redirect_uri' => 'http://www.example.com/my/subdir', 'client_id' => 'my_little_app', 'client_secret' => 'b', 'code'=> 'foo')
+            [
+                'grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE,
+                'redirect_uri' => 'http://www.example.com/my/subdir',
+                'client_id' => 'my_little_app',
+                'client_secret' => 'b',
+                'code'=> 'foo'
+            ]
         );
         $storedToken = new OAuth2AuthCode('my_little_app', '', time() + 60, null, null, 'http://www.example.com');
 
-        $mockStorage = $this->createBaseMock('OAuth2\IOAuth2GrantCode');
+        $mockStorage = $this->createBaseMock(IOAuth2GrantCode::class);
         $mockStorage->expects($this->any())
             ->method('getAuthCode')
-            ->will($this->returnValue($storedToken));
+            ->willReturn($storedToken);
 
         $this->fixture = new OAuth2($mockStorage);
         $response = $this->fixture->grantAccessToken($request);
@@ -41,17 +52,29 @@ public function testGrantAccessTokenWithGrantAuthCodeSuccess()
     /**
      * Tests OAuth2->grantAccessToken() with successful Auth code grant, but without redreict_uri in the input
      */
-    public function testGrantAccessTokenWithGrantAuthCodeSuccessWithoutRedirect()
+    public function testGrantAccessTokenWithGrantAuthCodeSuccessWithoutRedirect(): void
     {
         $request = new Request(
-            array('grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE, 'client_id' => 'my_little_app', 'client_secret' => 'b', 'code'=> 'foo')
+            [
+                'grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE,
+                'client_id' => 'my_little_app',
+                'client_secret' => 'b',
+                'code'=> 'foo'
+            ]
+        );
+        $storedToken = new OAuth2AuthCode(
+            'my_little_app',
+            '',
+            time() + 60,
+            null,
+            null,
+            'http://www.example.com'
         );
-        $storedToken = new OAuth2AuthCode('my_little_app', '', time() + 60, null, null, 'http://www.example.com');
 
-        $mockStorage = $this->createBaseMock('OAuth2\IOAuth2GrantCode');
+        $mockStorage = $this->createBaseMock(IOAuth2GrantCode::class);
         $mockStorage->expects($this->any())
             ->method('getAuthCode')
-            ->will($this->returnValue($storedToken));
+            ->willReturn($storedToken);
 
         $this->fixture = new OAuth2($mockStorage);
         $this->fixture->setVariable(OAuth2::CONFIG_ENFORCE_INPUT_REDIRECT, false);
@@ -63,28 +86,25 @@ public function testGrantAccessTokenWithGrantAuthCodeSuccessWithoutRedirect()
 
 // Utility methods
 
-    /**
-     *
-     * @param string $interfaceName
-     */
-    protected function createBaseMock($interfaceName)
+
+    protected function createBaseMock(string $interfaceName): MockObject
     {
         $client = new OAuth2Client('my_little_app');
 
         $mockStorage = $this->getMockBuilder($interfaceName)->getMock();
         $mockStorage->expects($this->any())
             ->method('getClient')
-            ->will($this->returnCallback(function ($id) use ($client) {
+            ->willReturnCallback(function ($id) use ($client) {
                 if ('my_little_app' === $id) {
                     return $client;
                 }
-            }));
+            });
         $mockStorage->expects($this->any())
             ->method('checkClientCredentials')
-            ->will($this->returnValue(true)); // Always return true for any combination of user/pass
+            ->willReturn(true); // Always return true for any combination of user/pass
         $mockStorage->expects($this->any())
             ->method('checkRestrictedGrantType')
-            ->will($this->returnValue(true)); // Always return true for any combination of user/pass
+            ->willReturn(true); // Always return true for any combination of user/pass
 
          return $mockStorage;
     }
diff --git a/tests/OAuth2Test.php b/tests/OAuth2Test.php
index fceef71..f999e18 100644
--- a/tests/OAuth2Test.php
+++ b/tests/OAuth2Test.php
@@ -1,5 +1,7 @@
 <?php
 
+namespace OAuth2\Tests;
+
 use OAuth2\OAuth2;
 use OAuth2\OAuth2ServerException;
 use OAuth2\Model\IOAuth2AccessToken;
@@ -9,12 +11,16 @@
 use OAuth2\Tests\Fixtures\OAuth2StorageStub;
 use OAuth2\Tests\Fixtures\OAuth2GrantCodeStub;
 use OAuth2\Tests\Fixtures\OAuth2GrantUserStub;
+use PHPUnit\Framework\TestCase;
 use Symfony\Component\HttpFoundation\Request;
+use OAuth2\OAuth2AuthenticateException;
+use OAuth2\IOAuth2Storage;
+use OAuth2\IOAuth2GrantCode;
 
 /**
  * OAuth2 test case.
  */
-class OAuth2Test extends PHPUnit_Framework_TestCase
+class OAuth2Test extends TestCase
 {
     /**
      * @var OAuth2
@@ -30,31 +36,31 @@ class OAuth2Test extends PHPUnit_Framework_TestCase
     /**
      * Tests OAuth2->verifyAccessToken() with a missing token
      */
-    public function testVerifyAccessTokenWithNoParam()
+    public function testVerifyAccessTokenWithNoParam(): void
     {
-        $mockStorage = $this->getMockBuilder('OAuth2\IOAuth2Storage')->getMock();
+        $mockStorage = $this->getMockBuilder(IOAuth2Storage::class)->getMock();
         $this->fixture = new OAuth2($mockStorage);
 
         $scope = null;
-        $this->setExpectedException('OAuth2\OAuth2AuthenticateException');
+        $this->expectException(OAuth2AuthenticateException::class);
         $this->fixture->verifyAccessToken('', $scope);
     }
 
     /**
      * Tests OAuth2->verifyAccessToken() with a invalid token
      */
-    public function testVerifyAccessTokenInvalidToken()
+    public function testVerifyAccessTokenInvalidToken(): void
     {
         // Set up the mock storage to say this token does not exist
-        $mockStorage = $this->getMockBuilder('OAuth2\IOAuth2Storage')->getMock();
+        $mockStorage = $this->getMockBuilder(IOAuth2Storage::class)->getMock();
         $mockStorage->expects($this->once())
             ->method('getAccessToken')
-            ->will($this->returnValue(false));
+            ->willReturn(false);
 
         $this->fixture = new OAuth2($mockStorage);
 
         $scope = null;
-        $this->setExpectedException('OAuth2\OAuth2AuthenticateException');
+        $this->expectException(OAuth2AuthenticateException::class);
         $this->fixture->verifyAccessToken($this->tokenId, $scope);
     }
 
@@ -62,19 +68,21 @@ public function testVerifyAccessTokenInvalidToken()
      * Tests OAuth2->verifyAccessToken() with a malformed token
      *
      * @dataProvider generateMalformedTokens
+     * @param IOAuth2AccessToken $token
+     * @throws OAuth2AuthenticateException
      */
-    public function testVerifyAccessTokenMalformedToken(IOAuth2AccessToken $token)
+    public function testVerifyAccessTokenMalformedToken(IOAuth2AccessToken $token): void
     {
         // Set up the mock storage to say this token does not exist
-        $mockStorage = $this->getMockBuilder('OAuth2\IOAuth2Storage')->getMock();
+        $mockStorage = $this->getMockBuilder(IOAuth2Storage::class)->getMock();
         $mockStorage->expects($this->once())
             ->method('getAccessToken')
-            ->will($this->returnValue($token));
+            ->willReturn($token);
 
         $this->fixture = new OAuth2($mockStorage);
 
         $scope = null;
-        $this->setExpectedException('OAuth2\OAuth2AuthenticateException');
+        $this->expectException(OAuth2AuthenticateException::class);
         $this->fixture->verifyAccessToken($this->tokenId, $scope);
     }
 
@@ -82,14 +90,19 @@ public function testVerifyAccessTokenMalformedToken(IOAuth2AccessToken $token)
      * Tests OAuth2->verifyAccessToken() with different expiry dates
      *
      * @dataProvider generateExpiryTokens
+     * @param IOAuth2AccessToken $token
+     * @param $expectedToPass
+     * @throws OAuth2AuthenticateException
      */
-    public function testVerifyAccessTokenCheckExpiry(IOAuth2AccessToken $token, $expectedToPass)
-    {
+    public function testVerifyAccessTokenCheckExpiry(
+        IOAuth2AccessToken $token,
+        $expectedToPass
+    ): void {
         // Set up the mock storage to say this token does not exist
-        $mockStorage = $this->getMockBuilder('OAuth2\IOAuth2Storage')->getMock();
+        $mockStorage = $this->getMockBuilder(IOAuth2Storage::class)->getMock();
         $mockStorage->expects($this->once())
             ->method('getAccessToken')
-            ->will($this->returnValue($token));
+            ->willReturn($token);
 
         $this->fixture = new OAuth2($mockStorage);
 
@@ -98,10 +111,10 @@ public function testVerifyAccessTokenCheckExpiry(IOAuth2AccessToken $token, $exp
         // When valid, we just want any sort of token
         if ($expectedToPass) {
             $actual = $this->fixture->verifyAccessToken($this->tokenId, $scope);
-            $this->assertNotEmpty($actual, "verifyAccessToken() was expected to PASS, but it failed");
-            $this->assertInstanceOf('OAuth2\Model\IOAuth2AccessToken', $actual);
+            $this->assertNotEmpty($actual, 'verifyAccessToken() was expected to PASS, but it failed');
+            $this->assertInstanceOf(IOAuth2AccessToken::class, $actual);
         } else {
-            $this->setExpectedException('OAuth2\OAuth2AuthenticateException');
+            $this->expectException(OAuth2AuthenticateException::class);
             $this->fixture->verifyAccessToken($this->tokenId, $scope);
         }
     }
@@ -110,24 +123,31 @@ public function testVerifyAccessTokenCheckExpiry(IOAuth2AccessToken $token, $exp
      * Tests OAuth2->verifyAccessToken() with different scopes
      *
      * @dataProvider generateScopes
+     * @param $scopeRequired
+     * @param IOAuth2AccessToken $token
+     * @param $expectedToPass
+     * @throws OAuth2AuthenticateException
      */
-    public function testVerifyAccessTokenCheckScope($scopeRequired, IOAuth2AccessToken $token, $expectedToPass)
-    {
+    public function testVerifyAccessTokenCheckScope(
+        $scopeRequired,
+        IOAuth2AccessToken $token,
+        $expectedToPass
+    ): void {
         // Set up the mock storage to say this token does not exist
-        $mockStorage = $this->getMockBuilder('OAuth2\IOAuth2Storage')->getMock();
+        $mockStorage = $this->getMockBuilder(IOAuth2Storage::class)->getMock();
         $mockStorage->expects($this->once())
             ->method('getAccessToken')
-            ->will($this->returnValue($token));
+            ->willReturn($token);
 
         $this->fixture = new OAuth2($mockStorage);
 
         // When valid, we just want any sort of token
         if ($expectedToPass) {
             $actual = $this->fixture->verifyAccessToken($this->tokenId, $scopeRequired);
-            $this->assertNotEmpty($actual, "verifyAccessToken() was expected to PASS, but it failed");
-            $this->assertInstanceOf('OAuth2\Model\IOAuth2AccessToken', $actual);
+            $this->assertNotEmpty($actual, 'verifyAccessToken() was expected to PASS, but it failed');
+            $this->assertInstanceOf(IOAuth2AccessToken::class, $actual);
         } else {
-            $this->setExpectedException('OAuth2\OAuth2AuthenticateException');
+            $this->expectException(OAuth2AuthenticateException::class);
             $this->fixture->verifyAccessToken($this->tokenId, $scopeRequired);
         }
     }
@@ -137,12 +157,12 @@ public function testVerifyAccessTokenCheckScope($scopeRequired, IOAuth2AccessTok
      *
      * @dataProvider generateEmptyDataForGrant
      */
-    public function testGrantAccessTokenMissingData($request)
+    public function testGrantAccessTokenMissingData($request): void
     {
-        $mockStorage = $this->getMockBuilder('OAuth2\IOAuth2Storage')->getMock();
+        $mockStorage = $this->getMockBuilder(IOAuth2Storage::class)->getMock();
         $this->fixture = new OAuth2($mockStorage);
 
-        $this->setExpectedException('OAuth2\OAuth2ServerException');
+        $this->expectException(OAuth2ServerException::class);
         $this->fixture->grantAccessToken($request);
     }
 
@@ -151,15 +171,15 @@ public function testGrantAccessTokenMissingData($request)
      *
      * Tests the different ways client credentials can be provided.
      */
-    public function testGrantAccessTokenCheckClientCredentials()
+    public function testGrantAccessTokenCheckClientCredentials(): void
     {
-        $mockStorage = $this->getMockBuilder('OAuth2\IOAuth2Storage')->getMock();
+        $mockStorage = $this->getMockBuilder(IOAuth2Storage::class)->getMock();
         $mockStorage->expects($this->any())
             ->method('getClient')
-            ->will($this->returnValue(new OAuth2Client('dev-abc')));
+            ->willReturn(new OAuth2Client('dev-abc'));
         $mockStorage->expects($this->any())
             ->method('checkClientCredentials')
-            ->will($this->returnValue(true)); // Always return true for any combination of user/pass
+            ->willReturn(true); // Always return true for any combination of user/pass
         $this->fixture = new OAuth2($mockStorage);
 
         $inputData = array('grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE);
@@ -169,29 +189,36 @@ public function testGrantAccessTokenCheckClientCredentials()
         try {
             $this->fixture->grantAccessToken($request);
             $this->fail('The expected exception OAuth2ServerException was not thrown');
-        } catch ( OAuth2ServerException $e ) {
+        } catch (OAuth2ServerException $e) {
             $this->assertEquals(OAuth2::ERROR_INVALID_CLIENT, $e->getMessage());
         }
 
         // Confirm Auth header
-        $authHeaders = array('PHP_AUTH_USER' => 'dev-abc', 'PHP_AUTH_PW' => 'pass');
-        $inputData = array('grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE, 'client_id' => 'dev-abc'); // When using auth, client_id must match
+        $authHeaders = ['PHP_AUTH_USER' => 'dev-abc', 'PHP_AUTH_PW' => 'pass'];
+        $inputData = [
+            'grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE,
+            'client_id' => 'dev-abc'
+        ]; // When using auth, client_id must match
         $request = $this->createRequest($inputData, $authHeaders);
         try {
             $this->fixture->grantAccessToken($request);
             $this->fail('The expected exception OAuth2ServerException was not thrown');
-        } catch ( OAuth2ServerException $e ) {
+        } catch (OAuth2ServerException $e) {
             $this->assertNotEquals(OAuth2::ERROR_INVALID_CLIENT, $e->getMessage());
         }
 
         // Confirm GET/POST
         $authHeaders = array();
-        $inputData = array('grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE, 'client_id' => 'dev-abc', 'client_secret' => 'foo'); // When using auth, client_id must match
+        $inputData = [
+            'grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE,
+            'client_id' => 'dev-abc',
+            'client_secret' => 'foo'
+        ]; // When using auth, client_id must match
         $request = $this->createRequest($inputData, $authHeaders);
         try {
             $this->fixture->grantAccessToken($request);
             $this->fail('The expected exception OAuth2ServerException was not thrown');
-        } catch ( OAuth2ServerException $e ) {
+        } catch (OAuth2ServerException $e) {
             $this->assertNotEquals(OAuth2::ERROR_INVALID_CLIENT, $e->getMessage());
         }
     }
@@ -200,10 +227,14 @@ public function testGrantAccessTokenCheckClientCredentials()
      * Tests OAuth2->grantAccessToken() with successful Client Credentials grant
      *
      */
-    public function testGrantAccessTokenWithClientCredentialsSuccess()
+    public function testGrantAccessTokenWithClientCredentialsSuccess(): void
     {
         $request = new Request(
-            array('grant_type' => OAuth2::GRANT_TYPE_CLIENT_CREDENTIALS, 'client_id' => 'my_little_app', 'client_secret' => 'b')
+            [
+                'grant_type' => OAuth2::GRANT_TYPE_CLIENT_CREDENTIALS,
+                'client_id' => 'my_little_app',
+                'client_secret' => 'b'
+            ]
         );
 
         $storage = new OAuth2StorageStub;
@@ -215,22 +246,25 @@ public function testGrantAccessTokenWithClientCredentialsSuccess()
         $response = $this->fixture->grantAccessToken($request);
 
         // Successful token grant will return a JSON encoded token WITHOUT a refresh token:
-        $this->assertRegExp('/^{"access_token":"[^"]+","expires_in":[^"]+,"token_type":"bearer","scope":null}$/', $response->getContent());
+        $this->assertRegExp(
+            '/^{"access_token":"[^"]+","expires_in":[^"]+,"token_type":"bearer","scope":null}$/',
+            $response->getContent()
+        );
     }
 
     /**
      * Tests OAuth2->grantAccessToken() with Auth code grant
      *
      */
-    public function testGrantAccessTokenWithGrantAuthCodeMandatoryParams()
+    public function testGrantAccessTokenWithGrantAuthCodeMandatoryParams(): void
     {
-        $mockStorage = $this->createBaseMock('OAuth2\IOAuth2GrantCode');
-        $mockStorage->expects($this->any())
+        $mockStorage = $this->createBaseMock(IOAuth2GrantCode::class);
+        $mockStorage
             ->method('getClient')
-            ->will($this->returnValue(new OAuth2Client('dev-abc')));
-        $mockStorage->expects($this->any())
+            ->willReturn(new OAuth2Client('dev-abc'));
+        $mockStorage
             ->method('checkClientCredentials')
-            ->will($this->returnValue(true)); // Always return true for any combination of user/pass
+            ->willReturn(true); // Always return true for any combination of user/pass
 
         $inputData = array('grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE, 'client_id' => 'a', 'client_secret' => 'b');
 
@@ -241,7 +275,7 @@ public function testGrantAccessTokenWithGrantAuthCodeMandatoryParams()
             $request = $this->createRequest($inputData + array('code' => 'foo'));
             $this->fixture->grantAccessToken($request);
             $this->fail('The expected exception OAuth2ServerException was not thrown');
-        } catch ( OAuth2ServerException $e ) {
+        } catch (OAuth2ServerException $e) {
             $this->assertEquals(OAuth2::ERROR_INVALID_REQUEST, $e->getMessage());
         }
         try {
@@ -249,7 +283,7 @@ public function testGrantAccessTokenWithGrantAuthCodeMandatoryParams()
             $request = $this->createRequest($inputData + array('redirect_uri' => 'foo'));
             $this->fixture->grantAccessToken($request);
             $this->fail('The expected exception OAuth2ServerException was not thrown');
-        } catch ( OAuth2ServerException $e ) {
+        } catch (OAuth2ServerException $e) {
             $this->assertEquals(OAuth2::ERROR_INVALID_REQUEST, $e->getMessage());
         }
     }
@@ -258,17 +292,23 @@ public function testGrantAccessTokenWithGrantAuthCodeMandatoryParams()
      * Tests OAuth2->grantAccessToken() with Auth code grant
      *
      */
-    public function testGrantAccessTokenWithGrantAuthCodeNoToken()
+    public function testGrantAccessTokenWithGrantAuthCodeNoToken(): void
     {
-        $mockStorage = $this->createBaseMock('OAuth2\IOAuth2GrantCode');
-        $mockStorage->expects($this->any())
+        $mockStorage = $this->createBaseMock(IOAuth2GrantCode::class);
+        $mockStorage
             ->method('getClient')
-            ->will($this->returnValue(new OAuth2Client('dev-abc')));
-        $mockStorage->expects($this->any())
+            ->willReturn(new OAuth2Client('dev-abc'));
+        $mockStorage
             ->method('checkClientCredentials')
-            ->will($this->returnValue(true)); // Always return true for any combination of user/pass
+            ->willReturn(true); // Always return true for any combination of user/pass
 
-        $inputData = array('grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE, 'client_id' => 'a', 'client_secret' => 'b', 'redirect_uri' => 'foo', 'code'=> 'foo');
+        $inputData = [
+            'grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE,
+            'client_id' => 'a',
+            'client_secret' => 'b',
+            'redirect_uri' => 'foo',
+            'code'=> 'foo'
+        ];
 
         // Ensure missing auth code raises an error
         try {
@@ -276,7 +316,7 @@ public function testGrantAccessTokenWithGrantAuthCodeNoToken()
             $request = $this->createRequest($inputData);
             $this->fixture->grantAccessToken($request);
             $this->fail('The expected exception OAuth2ServerException was not thrown');
-        } catch ( OAuth2ServerException $e ) {
+        } catch (OAuth2ServerException $e) {
             $this->assertEquals(OAuth2::ERROR_INVALID_GRANT, $e->getMessage());
         }
     }
@@ -1076,14 +1116,31 @@ public function getTestGetBearerTokenData()
         $data[] = array(new Request(array('access_token' => 'foo')), 'foo', true);
 
         foreach (array('POST', 'PUT', 'DELETE', 'FOOBAR') as $method) {
-
                 // $method without remove
-                $request = Request::create('/', $method, array(), array(), array(), array('CONTENT_TYPE' => 'application/x-www-form-urlencoded'), 'access_token=foo');
-                $data[] = array($request, 'foo');
+                $request = Request::create(
+                    '/',
+                    $method,
+                    [],
+                    [],
+                    [],
+                    ['CONTENT_TYPE' => 'application/x-www-form-urlencoded'],
+                    'access_token=foo'
+                );
+                $data[] = [$request, 'foo'];
 
                 // $method without remove and charset
-                $request = Request::create('/', $method, array(), array(), array(), array('CONTENT_TYPE' => 'application/x-www-form-urlencoded; charset=utf-8'), 'access_token=foo');
-                $data[] = array($request, 'foo');
+                $request = Request::create(
+                    '/',
+                    $method,
+                    [],
+                    [],
+                    [],
+                    [
+                        'CONTENT_TYPE' => 'application/x-www-form-urlencoded; charset=utf-8'
+                    ],
+                    'access_token=foo'
+                );
+                $data[] = [$request, 'foo'];
 
                 // $method without remove and additional information
                 $request = Request::create('/', $method, array(), array(), array(), array('CONTENT_TYPE' => 'application/x-www-form-urlencoded mode=baz'), 'access_token=foo');
@@ -1170,7 +1227,6 @@ public function getTestGetBearerTokenData()
         $data[] = array($request, 'foo');
 
         return $data;
-
     }
 
     // Utility methods
@@ -1178,18 +1234,21 @@ public function getTestGetBearerTokenData()
     /**
      *
      * @param string $interfaceName
+     * @return IOAuth2Storage
      */
-    protected function createBaseMock($interfaceName)
+    protected function createBaseMock($interfaceName) : IOAuth2Storage
     {
         $mockStorage = $this->getMockBuilder($interfaceName)->getMock();
-        $mockStorage->expects($this->any())
+        $mockStorage
             ->method('checkClientCredentials')
-            ->will($this->returnValue(true)); // Always return true for any combination of user/pass
-        $mockStorage->expects($this->any())
+            ->willReturn(true); // Always return true for any combination of user/pass
+        $mockStorage
             ->method('checkRestrictedGrantType')
-            ->will($this->returnValue(true)); // Always return true for any combination of user/pass
+            ->willReturn(true); // Always return true for any combination of user/pass
 
-         return $mockStorage;
+        /** @var IOAuth2Storage $mockStorage */
+        $theMock = $mockStorage;
+        return $theMock;
     }
 
     // Data Providers below:
@@ -1199,7 +1258,7 @@ protected function createBaseMock($interfaceName)
      *
      * Produces malformed access tokens
      */
-    public function generateMalformedTokens()
+    public function generateMalformedTokens(): array
     {
         return array(
             array(new OAuth2AccessToken(null, null, null)),
@@ -1211,16 +1270,16 @@ public function generateMalformedTokens()
      *
      * Produces malformed access tokens
      */
-    public function generateExpiryTokens()
+    public function generateExpiryTokens(): array
     {
         return array(
-            array(new OAuth2AccessToken('blah', '', time() - 30),                 false), // 30 seconds ago should fail
-            array(new OAuth2AccessToken('blah', '', time() - 1),                  false), // now-ish should fail
-            array(new OAuth2AccessToken('blah', '', 0),                           false), // 1970 should fail
-            array(new OAuth2AccessToken('blah', '', time() + 30),                 true),  // 30 seconds in the future should be valid
-            array(new OAuth2AccessToken('blah', '', time() + 86400),              true),  // 1 day in the future should be valid
-            array(new OAuth2AccessToken('blah', '', time() + (365 * 86400)),      true),  // 1 year should be valid
-            array(new OAuth2AccessToken('blah', '', time() + (10 * 365 * 86400)), true),  // 10 years should be valid
+            [new OAuth2AccessToken('blah', '', time() - 30),                 false], // 30 seconds ago should fail
+            [new OAuth2AccessToken('blah', '', time() - 1),                  false], // now-ish should fail
+            [new OAuth2AccessToken('blah', '', 0),                           false], // 1970 should fail
+            [new OAuth2AccessToken('blah', '', time() + 30),                 true],  // 30 seconds in the future should be valid
+            [new OAuth2AccessToken('blah', '', time() + 86400),              true],  // 1 day in the future should be valid
+            [new OAuth2AccessToken('blah', '', time() + (365 * 86400)),      true],  // 1 year should be valid
+            [new OAuth2AccessToken('blah', '', time() + (10 * 365 * 86400)), true],  // 10 years should be valid
         );
     }
 
@@ -1229,9 +1288,9 @@ public function generateExpiryTokens()
      *
      * Produces malformed access tokens
      */
-    public function generateScopes()
+    public function generateScopes(): array
     {
-        $token = function ($scope) {
+        $token = static function ($scope) {
             return new OAuth2AccessToken('blah', '', time() + 60, $scope);
         };
 
@@ -1258,32 +1317,33 @@ public function generateScopes()
     /**
      * Provider for OAuth2->grantAccessToken()
      */
-    public function generateEmptyDataForGrant()
+    public function generateEmptyDataForGrant(): array
     {
-        return array(
-            array(
-                $this->createRequest(array(), array())
-            ),
-            array(
-                $this->createRequest(array(), array('grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE)) // grant_type in auth headers should be ignored
-            ),
-            array(
-                $this->createRequest(array('not_grant_type' => 5), array())
-            ),
-        );
+        return [
+            [
+                $this->createRequest([], [])
+            ],
+            [
+                $this->createRequest(
+                    [],
+                    ['grant_type' => OAuth2::GRANT_TYPE_AUTH_CODE]
+                ) // grant_type in auth headers should be ignored
+            ],
+            [
+                $this->createRequest(['not_grant_type' => 5], [])
+            ],
+        ];
     }
 
-    public function createRequest(array $query = array(), array $headers = array())
+    public function createRequest(array $query = [], array $headers = []): Request
     {
-        $request = new Request(
-            $query      // _GET
-            , array()   // _REQUEST
-            , array()   // attributes
-            , array()   // _COOKIES
-            , array()   // _FILES
-            , $headers  // _SERVER
+        return new Request(
+            $query,      // _GET
+            [],   // _REQUEST
+            [],   // attributes
+            [],   // _COOKIES
+            [],  // _FILES
+            $headers  // _SERVER
         );
-
-        return $request;
     }
 }