diff --git a/src/Message/HeaderCollection.php b/src/Message/HeaderCollection.php
index 97c3c99..6367e66 100644
--- a/src/Message/HeaderCollection.php
+++ b/src/Message/HeaderCollection.php
@@ -7,51 +7,44 @@ use Iterator;
 
 /**
  * HeaderCollection provides case-insensitive access to lists of header values.
- *
- * This class is an internal class used by Message and is not intended for
- * direct use by consumers.
- *
+ **
  * HeaderCollection preserves the cases of keys as they are set, but treats key
  * access case insensitively.
  *
  * Any values added to HeaderCollection are added to list arrays. Subsequent
  * calls to add a value for a given key will append the new value to the list
  * array of values for that key.
+ *
+ * @internal This class is an internal class used by Message and is not intended
+ *   for direct use by consumers.
  */
 class HeaderCollection implements ArrayAccess, Iterator
 {
     /**
-     * @var array
-     *
      * Hash array mapping lowercase header names to original case header names.
+     *
+     * @var array<string, string>
      */
-    private $fields;
+    private $fields = [];
 
     /**
-     * @var array
-     *
      * Hash array mapping lowercase header names to values as string[]
+     *
+     * @var array<string, string[]>
      */
-    private $values;
+    private $values = [];
 
     /**
-     * @var string[]
-     *
      * List array of lowercase header names.
+     *
+     * @var string[]
      */
-    private $keys;
+    private $keys = [];
 
     /** @var int */
     private $position = 0;
 
-    public function __construct()
-    {
-        $this->keys = [];
-        $this->fields = [];
-        $this->values = [];
-    }
-
-    // ------------------------------------------------------------------------
+    // -------------------------------------------------------------------------
     // ArrayAccess
 
     /**
@@ -111,7 +104,7 @@ class HeaderCollection implements ArrayAccess, Iterator
         }
     }
 
-    // ------------------------------------------------------------------------
+    // -------------------------------------------------------------------------
     // Iterator
 
     public function current()
diff --git a/test/tests/unit/Message/HeaderCollectionTest.php b/test/tests/unit/Message/HeaderCollectionTest.php
index 730b575..568dcbc 100644
--- a/test/tests/unit/Message/HeaderCollectionTest.php
+++ b/test/tests/unit/Message/HeaderCollectionTest.php
@@ -1,20 +1,19 @@
 <?php
 
-namespace WellRESTed\Test\Unit\Message;
+namespace WellRESTed\Message;
 
-use WellRESTed\Message\HeaderCollection;
 use WellRESTed\Test\TestCase;
 
 class HeaderCollectionTest extends TestCase
 {
-    public function testAddsSingleHeaderAndIndicatesCaseInsensitiveIsset()
+    public function testAddsSingleHeaderAndIndicatesCaseInsensitiveIsset(): void
     {
         $collection = new HeaderCollection();
         $collection['Content-Type'] = 'application/json';
         $this->assertTrue(isset($collection['content-type']));
     }
 
-    public function testAddsMultipleHeadersAndIndicatesCaseInsensitiveIsset()
+    public function testAddsMultipleHeadersAndIndicatesCaseInsensitiveIsset(): void
     {
         $collection = new HeaderCollection();
         $collection['Set-Cookie'] = 'cat=Molly';
@@ -22,17 +21,18 @@ class HeaderCollectionTest extends TestCase
         $this->assertTrue(isset($collection['set-cookie']));
     }
 
-    public function testReturnsHeadersWithCaseInsensitiveHeaderName()
+    public function testReturnsHeadersWithCaseInsensitiveHeaderName(): void
     {
         $collection = new HeaderCollection();
         $collection['Set-Cookie'] = 'cat=Molly';
         $collection['SET-COOKIE'] = 'dog=Bear';
 
         $headers = $collection['set-cookie'];
-        $this->assertEquals(2, count(array_intersect($headers, ['cat=Molly', 'dog=Bear'])));
+        $matched = array_intersect($headers, ['cat=Molly', 'dog=Bear']);
+        $this->assertCount(2, $matched);
     }
 
-    public function testRemovesHeadersWithCaseInsensitiveHeaderName()
+    public function testRemovesHeadersWithCaseInsensitiveHeaderName(): void
     {
         $collection = new HeaderCollection();
         $collection['Set-Cookie'] = 'cat=Molly';
@@ -41,8 +41,7 @@ class HeaderCollectionTest extends TestCase
         $this->assertFalse(isset($collection['set-cookie']));
     }
 
-    /** @coversNothing */
-    public function testCloneMakesDeepCopyOfHeaders()
+    public function testCloneMakesDeepCopyOfHeaders(): void
     {
         $collection = new HeaderCollection();
         $collection['Set-Cookie'] = 'cat=Molly';
@@ -53,7 +52,7 @@ class HeaderCollectionTest extends TestCase
         $this->assertTrue(isset($collection['set-cookie']) && !isset($clone['set-cookie']));
     }
 
-    public function testIteratesWithOriginalKeys()
+    public function testIteratesWithOriginalKeys(): void
     {
         $collection = new HeaderCollection();
         $collection['Content-length'] = '100';
@@ -74,7 +73,7 @@ class HeaderCollectionTest extends TestCase
         $this->assertEquals(0, $countUnmatched);
     }
 
-    public function testIteratesWithOriginalKeysAndValues()
+    public function testIteratesWithOriginalKeysAndValues(): void
     {
         $collection = new HeaderCollection();
         $collection['Content-length'] = '100';