[10.x] Add PendingRequest withHeader() method (#47474)

* Add PendingRequest `withHeader()` method

* Space

* Test names

* Fix code style

* Update PendingRequest.php

---------

Co-authored-by: Taylor Otwell <taylor@laravel.com>

src/Illuminate/Http/Client/PendingRequest.php

@@ -393,6 +393,18 @@ public function withHeaders(array $headers)
         });
     }
 
+    /**
+     * Add the given header to the request.
+     *
+     * @param  string  $name
+     * @param  mixed  $value
+     * @return $this
+     */
+    public function withHeader($name, $value)
+    {
+        return $this->withHeaders([$name => $value]);
+    }
+
     /**
      * Replace the given headers on the request.
      *

tests/Http/HttpClientTest.php

@@ -909,6 +909,34 @@ public function testItCanReplaceHeadersWhenNoHeadersYetSet()
         });
     }
 
+    public function testCanConfirmSingleStringHeader()
+    {
+        $this->factory->fake();
+
+        $this->factory->withHeader('X-Test-Header', 'foo')->post('http://foo.com/json');
+
+        $this->factory->assertSent(function (Request $request) {
+            return $request->url() === 'http://foo.com/json' &&
+                $request->hasHeaders([
+                    'X-Test-Header' => 'foo',
+                ]);
+        });
+    }
+
+    public function testCanConfirmSingleArrayHeader()
+    {
+        $this->factory->fake();
+
+        $this->factory->withHeader('X-Test-ArrayHeader', ['bar', 'baz'])->post('http://foo.com/json');
+
+        $this->factory->assertSent(function (Request $request) {
+            return $request->url() === 'http://foo.com/json' &&
+                $request->hasHeaders([
+                    'X-Test-ArrayHeader' => ['bar', 'baz'],
+                ]);
+        });
+    }
+
     public function testExceptionAccessorOnSuccess()
     {
         $resp = new Response(new Psr7Response());