diff --git a/src/Message/Request.php b/src/Message/Request.php
index 33cddc0..9e7feac 100644
--- a/src/Message/Request.php
+++ b/src/Message/Request.php
@@ -33,11 +33,18 @@ class Request extends Message implements RequestInterface
     /**
      * Create a new Request.
      *
-     * @see \WellRESTed\Message\Message
-     * @param string|UriInterface $uri
+     * $headers is an optional associative array with header field names as
+     * (string) keys and lists of header field values (string[]) as values.
+     *
+     * If no StreamInterface is provided for $body, the instance will create
+     * a NullStream instance for the message body.
+     *
      * @param string $method
-     * @param array $headers
-     * @param StreamInterface|null $body
+     * @param string|UriInterface $uri
+     * @param array $headers Associative array with header field names as
+     *     (string) keys and lists of header field values (string[]) as values.
+     * @param StreamInterface|null $body A stream representation of the message
+     *     entity body
      */
     public function __construct(
         string $method = 'GET',
diff --git a/src/Message/Response.php b/src/Message/Response.php
index 2269186..99a02c2 100644
--- a/src/Message/Response.php
+++ b/src/Message/Response.php
@@ -35,6 +35,7 @@ class Response extends Message implements ResponseInterface
      * a NullStream instance for the message body.
      *
      * @see \WellRESTed\Message\Message
+     *
      * @param int $statusCode
      * @param array $headers
      * @param StreamInterface|null $body
@@ -58,7 +59,7 @@ class Response extends Message implements ResponseInterface
      * The status code is a 3-digit integer result code of the server's attempt
      * to understand and satisfy the request.
      *
-     * @return integer Status code.
+     * @return int Status code.
      */
     public function getStatusCode()
     {
diff --git a/test/tests/unit/Message/MessageTest.php b/test/tests/unit/Message/MessageTest.php
index 093331e..03c9c62 100644
--- a/test/tests/unit/Message/MessageTest.php
+++ b/test/tests/unit/Message/MessageTest.php
@@ -1,38 +1,27 @@
 <?php
 
-namespace WellRESTed\Test\Unit\Message;
+namespace WellRESTed\Message;
 
 use InvalidArgumentException;
-use WellRESTed\Message\Message;
-use WellRESTed\Message\Response;
-use WellRESTed\Message\Stream;
 use WellRESTed\Test\TestCase;
 
 class MessageTest extends TestCase
 {
-    /** @var Message */
-    private $message;
-
-    public function setUp(): void
-    {
-        $this->message = new Response();
-    }
-
-    public function testSetsHeadersOnConstruction()
+    public function testSetsHeadersOnConstruction(): void
     {
         $headers = ['X-foo' => ['bar', 'baz']];
         $message = new Response(200, $headers);
         $this->assertEquals(['bar', 'baz'], $message->getHeader('X-foo'));
     }
 
-    public function testSetsBodyOnConstruction()
+    public function testSetsBodyOnConstruction(): void
     {
         $body = new Stream('Hello, world');
         $message = new Response(200, [], $body);
         $this->assertSame($body, $message->getBody());
     }
 
-    public function testCloneMakesDeepCopyOfHeaders()
+    public function testCloneMakesDeepCopyOfHeaders(): void
     {
         $message1 = (new Response())
             ->withHeader('Content-type', 'text/plain');
@@ -48,20 +37,20 @@ class MessageTest extends TestCase
     // ------------------------------------------------------------------------
     // Protocol Version
 
-    public function testGetProtocolVersionReturnsProtocolVersion1Point1ByDefault()
+    public function testGetProtocolVersionReturnsProtocolVersion1Point1ByDefault(): void
     {
         $message = new Response();
         $this->assertEquals('1.1', $message->getProtocolVersion());
     }
 
-    public function testGetProtocolVersionReturnsProtocolVersion()
+    public function testGetProtocolVersionReturnsProtocolVersion(): void
     {
         $message = (new Response())
             ->withProtocolVersion('1.0');
         $this->assertEquals('1.0', $message->getProtocolVersion());
     }
 
-    public function testGetProtocolVersionReplacesProtocolVersion()
+    public function testGetProtocolVersionReplacesProtocolVersion(): void
     {
         $message = (new Response())
             ->withProtocolVersion('1.0');
@@ -71,8 +60,12 @@ class MessageTest extends TestCase
     // ------------------------------------------------------------------------
     // Headers
 
-    /** @dataProvider validHeaderValueProvider */
-    public function testWithHeaderReplacesHeader($expected, $value)
+    /**
+     * @dataProvider validHeaderValueProvider
+     * @param array $expected
+     * @param mixed $value
+     */
+    public function testWithHeaderReplacesHeader(array $expected, $value): void
     {
         $message = (new Response())
             ->withHeader('X-foo', 'Original value')
@@ -80,7 +73,7 @@ class MessageTest extends TestCase
         $this->assertEquals($expected, $message->getHeader('X-foo'));
     }
 
-    public function validHeaderValueProvider()
+    public function validHeaderValueProvider(): array
     {
         return [
             [['0'], 0],
@@ -90,15 +83,17 @@ class MessageTest extends TestCase
 
     /**
      * @dataProvider invalidHeaderProvider
+     * @param mixed $name
+     * @param mixed $value
      */
-    public function testWithHeaderThrowsExceptionWithInvalidArgument($name, $value)
+    public function testWithHeaderThrowsExceptionWithInvalidArgument($name, $value): void
     {
         $this->expectException(InvalidArgumentException::class);
-        $message = (new Response())
+        (new Response())
             ->withHeader($name, $value);
     }
 
-    public function invalidHeaderProvider()
+    public function invalidHeaderProvider(): array
     {
         return [
             [0, 1024],
@@ -107,14 +102,14 @@ class MessageTest extends TestCase
         ];
     }
 
-    public function testWithAddedHeaderSetsHeader()
+    public function testWithAddedHeaderSetsHeader(): void
     {
         $message = (new Response())
             ->withAddedHeader('Content-type', 'application/json');
         $this->assertEquals(['application/json'], $message->getHeader('Content-type'));
     }
 
-    public function testWithAddedHeaderAppendsValue()
+    public function testWithAddedHeaderAppendsValue(): void
     {
         $message = (new Response())
             ->withAddedHeader('Set-Cookie', ['cat=Molly'])
@@ -126,7 +121,7 @@ class MessageTest extends TestCase
         );
     }
 
-    public function testWithoutHeaderRemovesHeader()
+    public function testWithoutHeaderRemovesHeader(): void
     {
         $message = (new Response())
             ->withHeader('Content-type', 'application/json')
@@ -134,20 +129,20 @@ class MessageTest extends TestCase
         $this->assertFalse($message->hasHeader('Content-type'));
     }
 
-    public function testGetHeaderReturnsEmptyArrayForUnsetHeader()
+    public function testGetHeaderReturnsEmptyArrayForUnsetHeader(): void
     {
         $message = new Response();
         $this->assertEquals([], $message->getHeader('X-name'));
     }
 
-    public function testGetHeaderReturnsSingleHeader()
+    public function testGetHeaderReturnsSingleHeader(): void
     {
         $message = (new Response())
             ->withAddedHeader('Content-type', 'application/json');
         $this->assertEquals(['application/json'], $message->getHeader('Content-type'));
     }
 
-    public function testGetHeaderReturnsMultipleValuesForHeader()
+    public function testGetHeaderReturnsMultipleValuesForHeader(): void
     {
         $message = (new Response())
             ->withAddedHeader('X-name', 'cat=Molly')
@@ -155,13 +150,13 @@ class MessageTest extends TestCase
         $this->assertEquals(['cat=Molly', 'dog=Bear'], $message->getHeader('X-name'));
     }
 
-    public function testGetHeaderLineReturnsEmptyStringForUnsetHeader()
+    public function testGetHeaderLineReturnsEmptyStringForUnsetHeader(): void
     {
         $message = new Response();
         $this->assertSame('', $message->getHeaderLine('X-not-set'));
     }
 
-    public function testGetHeaderLineReturnsMultipleHeadersJoinedByCommas()
+    public function testGetHeaderLineReturnsMultipleHeadersJoinedByCommas(): void
     {
         $message = (new Response())
             ->withAddedHeader('X-name', 'cat=Molly')
@@ -169,20 +164,20 @@ class MessageTest extends TestCase
         $this->assertEquals('cat=Molly, dog=Bear', $message->getHeaderLine('X-name'));
     }
 
-    public function testHasHeaderReturnsTrueWhenHeaderIsSet()
+    public function testHasHeaderReturnsTrueWhenHeaderIsSet(): void
     {
         $message = (new Response())
             ->withHeader('Content-type', 'application/json');
         $this->assertTrue($message->hasHeader('Content-type'));
     }
 
-    public function testHasHeaderReturnsFalseWhenHeaderIsNotSet()
+    public function testHasHeaderReturnsFalseWhenHeaderIsNotSet(): void
     {
         $message = new Response();
         $this->assertFalse($message->hasHeader('Content-type'));
     }
 
-    public function testGetHeadersReturnOriginalHeaderNamesAsKeys()
+    public function testGetHeadersReturnOriginalHeaderNamesAsKeys(): void
     {
         $message = (new Response())
             ->withHeader('Set-Cookie', 'cat=Molly')
@@ -201,7 +196,7 @@ class MessageTest extends TestCase
         $this->assertEquals(0, $countUnmatched);
     }
 
-    public function testGetHeadersReturnOriginalHeaderNamesAndValues()
+    public function testGetHeadersReturnOriginalHeaderNamesAndValues(): void
     {
         $message = (new Response())
             ->withHeader('Set-Cookie', 'cat=Molly')
@@ -231,13 +226,13 @@ class MessageTest extends TestCase
     // ------------------------------------------------------------------------
     // Body
 
-    public function testGetBodyReturnsEmptyStreamByDefault()
+    public function testGetBodyReturnsEmptyStreamByDefault(): void
     {
         $message = new Response();
         $this->assertEquals('', (string) $message->getBody());
     }
 
-    public function testGetBodyReturnsAttachedStream()
+    public function testGetBodyReturnsAttachedStream(): void
     {
         $stream = new Stream('Hello, world!');
 
diff --git a/test/tests/unit/Message/RequestTest.php b/test/tests/unit/Message/RequestTest.php
index ad81f3c..3474a40 100644
--- a/test/tests/unit/Message/RequestTest.php
+++ b/test/tests/unit/Message/RequestTest.php
@@ -1,11 +1,8 @@
 <?php
 
-namespace WellRESTed\Test\Unit\Message;
+namespace WellRESTed\Message;
 
 use InvalidArgumentException;
-use WellRESTed\Message\NullStream;
-use WellRESTed\Message\Request;
-use WellRESTed\Message\Uri;
 use WellRESTed\Test\TestCase;
 
 class RequestTest extends TestCase
@@ -13,34 +10,34 @@ class RequestTest extends TestCase
     // ------------------------------------------------------------------------
     // Construction
 
-    public function testCreatesInstanceWithNoParameters()
+    public function testCreatesInstanceWithNoParameters(): void
     {
         $request = new Request();
         $this->assertNotNull($request);
     }
 
-    public function testCreatesInstanceWithMethod()
+    public function testCreatesInstanceWithMethod(): void
     {
         $method = 'POST';
         $request = new Request($method);
         $this->assertSame($method, $request->getMethod());
     }
 
-    public function testCreatesInstanceWithUri()
+    public function testCreatesInstanceWithUri(): void
     {
         $uri = new Uri();
         $request = new Request('GET', $uri);
         $this->assertSame($uri, $request->getUri());
     }
 
-    public function testCreatesInstanceWithStringUri()
+    public function testCreatesInstanceWithStringUri(): void
     {
         $uri = 'http://localhost:8080';
         $request = new Request('GET', $uri);
         $this->assertSame($uri, (string) $request->getUri());
     }
 
-    public function testSetsHeadersOnConstruction()
+    public function testSetsHeadersOnConstruction(): void
     {
         $request = new Request('GET', '/', [
             'X-foo' => ['bar', 'baz']
@@ -48,7 +45,7 @@ class RequestTest extends TestCase
         $this->assertEquals(['bar', 'baz'], $request->getHeader('X-foo'));
     }
 
-    public function testSetsBodyOnConstruction()
+    public function testSetsBodyOnConstruction(): void
     {
         $body = new NullStream();
         $request = new Request('GET', '/', [], $body);
@@ -58,14 +55,14 @@ class RequestTest extends TestCase
     // ------------------------------------------------------------------------
     // Request Target
 
-    public function testGetRequestTargetPrefersExplicitRequestTarget()
+    public function testGetRequestTargetPrefersExplicitRequestTarget(): void
     {
         $request = new Request();
         $request = $request->withRequestTarget('*');
         $this->assertEquals('*', $request->getRequestTarget());
     }
 
-    public function testGetRequestTargetUsesOriginFormOfUri()
+    public function testGetRequestTargetUsesOriginFormOfUri(): void
     {
         $uri = new Uri('/my/path?cat=Molly&dog=Bear');
         $request = new Request();
@@ -73,13 +70,13 @@ class RequestTest extends TestCase
         $this->assertEquals('/my/path?cat=Molly&dog=Bear', $request->getRequestTarget());
     }
 
-    public function testGetRequestTargetReturnsSlashByDefault()
+    public function testGetRequestTargetReturnsSlashByDefault(): void
     {
         $request = new Request();
         $this->assertEquals('/', $request->getRequestTarget());
     }
 
-    public function testWithRequestTargetCreatesNewInstance()
+    public function testWithRequestTargetCreatesNewInstance(): void
     {
         $request = new Request();
         $request = $request->withRequestTarget('*');
@@ -89,13 +86,13 @@ class RequestTest extends TestCase
     // ------------------------------------------------------------------------
     // Method
 
-    public function testGetMethodReturnsGetByDefault()
+    public function testGetMethodReturnsGetByDefault(): void
     {
         $request = new Request();
         $this->assertEquals('GET', $request->getMethod());
     }
 
-    public function testWithMethodCreatesNewInstance()
+    public function testWithMethodCreatesNewInstance(): void
     {
         $request = new Request();
         $request = $request->withMethod('POST');
@@ -104,15 +101,16 @@ class RequestTest extends TestCase
 
     /**
      * @dataProvider invalidMethodProvider
+     * @param mixed $method
      */
-    public function testWithMethodThrowsExceptionOnInvalidMethod($method)
+    public function testWithMethodThrowsExceptionOnInvalidMethod($method): void
     {
         $this->expectException(InvalidArgumentException::class);
         $request = new Request();
         $request->withMethod($method);
     }
 
-    public function invalidMethodProvider()
+    public function invalidMethodProvider(): array
     {
         return [
             [0],
@@ -124,14 +122,14 @@ class RequestTest extends TestCase
     // ------------------------------------------------------------------------
     // Request URI
 
-    public function testGetUriReturnsEmptyUriByDefault()
+    public function testGetUriReturnsEmptyUriByDefault(): void
     {
         $request = new Request();
         $uri = new Uri();
         $this->assertEquals($uri, $request->getUri());
     }
 
-    public function testWithUriCreatesNewInstance()
+    public function testWithUriCreatesNewInstance(): void
     {
         $uri = new Uri();
         $request = new Request();
@@ -139,7 +137,7 @@ class RequestTest extends TestCase
         $this->assertSame($uri, $request->getUri());
     }
 
-    public function testWithUriPreservesOriginalRequest()
+    public function testWithUriPreservesOriginalRequest(): void
     {
         $uri1 = new Uri();
         $uri2 = new Uri();
@@ -154,7 +152,7 @@ class RequestTest extends TestCase
         $this->assertNotEquals($request1->getHeader('Accept'), $request2->getHeader('Accept'));
     }
 
-    public function testWithUriUpdatesHostHeader()
+    public function testWithUriUpdatesHostHeader(): void
     {
         $hostname = 'bar.com';
         $uri = new uri("http://$hostname");
@@ -165,7 +163,7 @@ class RequestTest extends TestCase
         $this->assertSame([$hostname], $request->getHeader('Host'));
     }
 
-    public function testWithUriDoesNotUpdatesHostHeaderWhenUriHasNoHost()
+    public function testWithUriDoesNotUpdatesHostHeaderWhenUriHasNoHost(): void
     {
         $hostname = 'foo.com';
         $uri = new Uri();
@@ -176,7 +174,7 @@ class RequestTest extends TestCase
         $this->assertSame([$hostname], $request->getHeader('Host'));
     }
 
-    public function testPreserveHostUpdatesHostHeaderWhenHeaderIsOriginallyMissing()
+    public function testPreserveHostUpdatesHostHeaderWhenHeaderIsOriginallyMissing(): void
     {
         $hostname = 'foo.com';
         $uri = new uri("http://$hostname");
@@ -186,7 +184,7 @@ class RequestTest extends TestCase
         $this->assertSame([$hostname], $request->getHeader('Host'));
     }
 
-    public function testPreserveHostDoesNotUpdatesWhenBothAreMissingHosts()
+    public function testPreserveHostDoesNotUpdatesWhenBothAreMissingHosts(): void
     {
         $uri = new Uri();
 
@@ -195,7 +193,7 @@ class RequestTest extends TestCase
         $this->assertSame([], $request->getHeader('Host'));
     }
 
-    public function testPreserveHostDoesNotUpdateHostHeader()
+    public function testPreserveHostDoesNotUpdateHostHeader(): void
     {
         $hostname = 'foo.com';
         $uri = new uri('http://bar.com');
diff --git a/test/tests/unit/Message/ResponseTest.php b/test/tests/unit/Message/ResponseTest.php
index 9f119e5..57b4e35 100644
--- a/test/tests/unit/Message/ResponseTest.php
+++ b/test/tests/unit/Message/ResponseTest.php
@@ -1,9 +1,7 @@
 <?php
 
-namespace WellRESTed\Test\Unit\Message;
+namespace WellRESTed\Message;
 
-use WellRESTed\Message\NullStream;
-use WellRESTed\Message\Response;
 use WellRESTed\Test\TestCase;
 
 class ResponseTest extends TestCase
@@ -11,13 +9,13 @@ class ResponseTest extends TestCase
     // ------------------------------------------------------------------------
     // Construction
 
-    public function testSetsStatusCodeOnConstruction()
+    public function testSetsStatusCodeOnConstruction(): void
     {
         $response = new Response(200);
         $this->assertSame(200, $response->getStatusCode());
     }
 
-    public function testSetsHeadersOnConstruction()
+    public function testSetsHeadersOnConstruction(): void
     {
         $response = new Response(200, [
             'X-foo' => ['bar','baz']
@@ -25,7 +23,7 @@ class ResponseTest extends TestCase
         $this->assertEquals(['bar','baz'], $response->getHeader('X-foo'));
     }
 
-    public function testSetsBodyOnConstruction()
+    public function testSetsBodyOnConstruction(): void
     {
         $body = new NullStream();
         $response = new Response(200, [], $body);
@@ -35,22 +33,30 @@ class ResponseTest extends TestCase
     // ------------------------------------------------------------------------
     // Status and Reason Phrase
 
-    public function testCreatesNewInstanceWithStatusCode()
+    public function testCreatesNewInstanceWithStatusCode(): void
     {
         $response = new Response();
         $copy = $response->withStatus(200);
         $this->assertEquals(200, $copy->getStatusCode());
     }
 
-    /** @dataProvider statusProvider */
-    public function testCreatesNewInstanceWithReasonPhrase($code, $reasonPhrase, $expected)
-    {
+    /**
+     * @dataProvider statusProvider
+     * @param int $code
+     * @param string|null $reasonPhrase
+     * @param string $expected
+     */
+    public function testCreatesNewInstanceWithReasonPhrase(
+        int $code,
+        ?string $reasonPhrase,
+        string $expected
+    ): void {
         $response = new Response();
         $copy = $response->withStatus($code, $reasonPhrase);
         $this->assertEquals($expected, $copy->getReasonPhrase());
     }
 
-    public function statusProvider()
+    public function statusProvider(): array
     {
         return [
             [100, null, 'Continue'],
@@ -95,7 +101,7 @@ class ResponseTest extends TestCase
         ];
     }
 
-    public function testWithStatusCodePreservesOriginalResponse()
+    public function testWithStatusCodePreservesOriginalResponse(): void
     {
         $response1 = new Response();
         $response1 = $response1->withStatus(200);
diff --git a/test/tests/unit/Message/ServerRequestTest.php b/test/tests/unit/Message/ServerRequestTest.php
index 22916f2..10fcc60 100644
--- a/test/tests/unit/Message/ServerRequestTest.php
+++ b/test/tests/unit/Message/ServerRequestTest.php
@@ -10,7 +10,7 @@ class ServerRequestTest extends TestCase
     // ------------------------------------------------------------------------
     // Server Params
 
-    public function testGetServerParamsReturnsEmptyArrayByDefault()
+    public function testGetServerParamsReturnsEmptyArrayByDefault(): void
     {
         $request = new ServerRequest();
         $this->assertEquals([], $request->getServerParams());
@@ -19,13 +19,13 @@ class ServerRequestTest extends TestCase
     // ------------------------------------------------------------------------
     // Cookies
 
-    public function testGetCookieParamsReturnsEmptyArrayByDefault()
+    public function testGetCookieParamsReturnsEmptyArrayByDefault(): void
     {
         $request = new ServerRequest();
         $this->assertEquals([], $request->getCookieParams());
     }
 
-    public function testWithCookieParamsCreatesNewInstanceWithCookies()
+    public function testWithCookieParamsCreatesNewInstanceWithCookies(): void
     {
         $cookies = [
             'cat' => 'Oscar'
@@ -41,13 +41,13 @@ class ServerRequestTest extends TestCase
     // ------------------------------------------------------------------------
     // Query
 
-    public function testGetQueryParamsReturnsEmptyArrayByDefault()
+    public function testGetQueryParamsReturnsEmptyArrayByDefault(): void
     {
         $request = new ServerRequest();
         $this->assertEquals([], $request->getQueryParams());
     }
 
-    public function testWithQueryParamsCreatesNewInstance()
+    public function testWithQueryParamsCreatesNewInstance(): void
     {
         $query = [
             'cat' => 'Aggie'
@@ -63,13 +63,13 @@ class ServerRequestTest extends TestCase
     // ------------------------------------------------------------------------
     // Uploaded Files
 
-    public function testGetUploadedFilesReturnsEmptyArrayByDefault()
+    public function testGetUploadedFilesReturnsEmptyArrayByDefault(): void
     {
         $request = new ServerRequest();
         $this->assertEquals([], $request->getUploadedFiles());
     }
 
-    public function testWithUploadedFilesCreatesNewInstance()
+    public function testWithUploadedFilesCreatesNewInstance(): void
     {
         $uploadedFiles = [
             'file' => new UploadedFile('index.html', 'text/html', 524, '/tmp/php9hNlHe', 0)
@@ -80,15 +80,18 @@ class ServerRequestTest extends TestCase
         $this->assertNotSame($request2, $request1);
     }
 
-    /** @dataProvider validUploadedFilesProvider */
-    public function testWithUploadedFilesStoresPassedUploadedFiles($uploadedFiles)
+    /**
+     * @dataProvider validUploadedFilesProvider
+     * @param array $uploadedFiles
+     */
+    public function testWithUploadedFilesStoresPassedUploadedFiles(array $uploadedFiles): void
     {
         $request = new ServerRequest();
         $request = $request->withUploadedFiles($uploadedFiles);
         $this->assertSame($uploadedFiles, $request->getUploadedFiles());
     }
 
-    public function validUploadedFilesProvider()
+    public function validUploadedFilesProvider(): array
     {
         return [
             [[]],
@@ -113,8 +116,9 @@ class ServerRequestTest extends TestCase
 
     /**
      * @dataProvider invalidUploadedFilesProvider
+     * @param array $uploadedFiles
      */
-    public function testWithUploadedFilesThrowsExceptionWithInvalidTree($uploadedFiles)
+    public function testWithUploadedFilesThrowsExceptionWithInvalidTree(array $uploadedFiles): void
     {
         $this->expectException(InvalidArgumentException::class);
         $request = new ServerRequest();
@@ -185,13 +189,13 @@ class ServerRequestTest extends TestCase
     // ------------------------------------------------------------------------
     // Parsed Body
 
-    public function testGetParsedBodyReturnsNullByDefault()
+    public function testGetParsedBodyReturnsNullByDefault(): void
     {
         $request = new ServerRequest();
         $this->assertNull($request->getParsedBody());
     }
 
-    public function testWithParsedBodyCreatesNewInstance()
+    public function testWithParsedBodyCreatesNewInstance(): void
     {
         $body = [
             'guinea_pig' => 'Clyde'
@@ -206,8 +210,9 @@ class ServerRequestTest extends TestCase
 
     /**
      * @dataProvider invalidParsedBodyProvider
+     * @param mixed $body
      */
-    public function testWithParsedBodyThrowsExceptionWithInvalidType($body)
+    public function testWithParsedBodyThrowsExceptionWithInvalidType($body): void
     {
         $this->expectException(InvalidArgumentException::class);
         $request = new ServerRequest();
@@ -222,7 +227,7 @@ class ServerRequestTest extends TestCase
         ];
     }
 
-    public function testCloneMakesDeepCopiesOfParsedBody()
+    public function testCloneMakesDeepCopiesOfParsedBody(): void
     {
         $body = (object) [
             'cat' => 'Dog'
@@ -241,13 +246,13 @@ class ServerRequestTest extends TestCase
     // ------------------------------------------------------------------------
     // Attributes
 
-    public function testGetAttributesReturnsEmptyArrayByDefault()
+    public function testGetAttributesReturnsEmptyArrayByDefault(): void
     {
         $request = new ServerRequest();
         $this->assertEquals([], $request->getAttributes());
     }
 
-    public function testGetAttributesReturnsAllAttributes()
+    public function testGetAttributesReturnsAllAttributes(): void
     {
         $request = new ServerRequest();
         $request = $request->withAttribute('cat', 'Molly');
@@ -259,20 +264,20 @@ class ServerRequestTest extends TestCase
         $this->assertEquals($expected, $request->getAttributes());
     }
 
-    public function testGetAttributeReturnsDefaultIfNotSet()
+    public function testGetAttributeReturnsDefaultIfNotSet(): void
     {
         $request = new ServerRequest();
         $this->assertEquals('Oscar', $request->getAttribute('cat', 'Oscar'));
     }
 
-    public function testWithAttributeCreatesNewInstance()
+    public function testWithAttributeCreatesNewInstance(): void
     {
         $request = new ServerRequest();
         $request = $request->withAttribute('cat', 'Molly');
         $this->assertEquals('Molly', $request->getAttribute('cat'));
     }
 
-    public function testWithAttributePreserversOtherAttributes()
+    public function testWithAttributePreserversOtherAttributes(): void
     {
         $request = new ServerRequest();
         $request = $request->withAttribute('cat', 'Molly');
@@ -284,14 +289,14 @@ class ServerRequestTest extends TestCase
         $this->assertEquals($expected, $request->getAttributes());
     }
 
-    public function testWithoutAttributeCreatesNewInstance()
+    public function testWithoutAttributeCreatesNewInstance(): void
     {
         $request = new ServerRequest();
         $request = $request->withAttribute('cat', 'Molly');
         $this->assertNotEquals($request, $request->withoutAttribute('cat'));
     }
 
-    public function testWithoutAttributeRemovesAttribute()
+    public function testWithoutAttributeRemovesAttribute(): void
     {
         $request = new ServerRequest();
         $request = $request->withAttribute('cat', 'Molly');
@@ -299,7 +304,7 @@ class ServerRequestTest extends TestCase
         $this->assertEquals('Oscar', $request->getAttribute('cat', 'Oscar'));
     }
 
-    public function testWithoutAttributePreservesOtherAttributes()
+    public function testWithoutAttributePreservesOtherAttributes(): void
     {
         $request = new ServerRequest();
         $request = $request->withAttribute('cat', 'Molly');