Refactor HTTP testing API and improve header handling

- Remove testing assertion methods from Http class and move to TestingHttpHandler
- Add comprehensive HttpTestingAssistant class for dedicated testing functionality
- Update test files to use TestingHttpHandler assertions directly
- Fix MockedRequest header handling to support multiple values for same header name
- Improve code organization by separating testing concerns from main Http API

Author: rcalicdan

src/Api/Http.php

@@ -155,13 +155,20 @@ public static function getTestingHandler(): TestingHttpHandler
     }
 
     /**
-     * Check if Http is currently in testing mode.
+     * Convenience method to quickly mock a request in testing mode.
+     * Follows Laravel's Http::fake() pattern.
+     *
+     * @param  string  $method  HTTP method to mock (default: '*' for any)
      *
-     * @return bool True if in testing mode, false otherwise
+     * @throws \RuntimeException If not in testing mode
      */
-    public static function isTesting(): bool
+    public static function mock(string $method = '*'): MockRequestBuilder
     {
-        return self::$isTesting;
+        if (! self::$isTesting || self::$testingInstance === null) {
+            throw new \RuntimeException('Not in testing mode. Call Http::testing() first.');
+        }
+
+        return self::$testingInstance->mock($method);
     }
 
     /**
@@ -202,73 +209,6 @@ public static function setInstance(HttpHandler $handler): void
         }
     }
 
-    /**
-     * Convenience method to quickly mock a request in testing mode.
-     *
-     * @param  string  $method  HTTP method to mock (default: '*' for any)
-     *
-     * @throws \RuntimeException If not in testing mode
-     */
-    public static function mock(string $method = '*'): MockRequestBuilder
-    {
-        if (! self::$isTesting || self::$testingInstance === null) {
-            throw new \RuntimeException('Not in testing mode. Call Http::testing() first.');
-        }
-
-        return self::$testingInstance->mock($method);
-    }
-
-    /**
-     * Assert that a specific request was made during testing.
-     *
-     * @param  string  $method  HTTP method
-     * @param  string  $url  URL pattern
-     * @param  array<string, mixed>  $options  Additional matching options
-     *
-     * @throws \RuntimeException If not in testing mode
-     * @throws \Exception If assertion fails
-     */
-    public static function assertRequestMade(string $method, string $url, array $options = []): void
-    {
-        if (! self::$isTesting || self::$testingInstance === null) {
-            throw new \RuntimeException('Not in testing mode. Call Http::testing() first.');
-        }
-
-        self::$testingInstance->assertRequestMade($method, $url, $options);
-    }
-
-    /**
-     * Assert that no HTTP requests were made during testing.
-     *
-     * @throws \RuntimeException If not in testing mode
-     * @throws \Exception If assertion fails
-     */
-    public static function assertNoRequestsMade(): void
-    {
-        if (! self::$isTesting || self::$testingInstance === null) {
-            throw new \RuntimeException('Not in testing mode. Call Http::testing() first.');
-        }
-
-        self::$testingInstance->assertNoRequestsMade();
-    }
-
-    /**
-     * Assert a specific number of requests were made during testing.
-     *
-     * @param  int  $expected  Expected number of requests
-     *
-     * @throws \RuntimeException If not in testing mode
-     * @throws \Exception If assertion fails
-     */
-    public static function assertRequestCount(int $expected): void
-    {
-        if (! self::$isTesting || self::$testingInstance === null) {
-            throw new \RuntimeException('Not in testing mode. Call Http::testing() first.');
-        }
-
-        self::$testingInstance->assertRequestCount($expected);
-    }
-
     /**
      * Magic method to handle dynamic static calls.
      *
@@ -298,6 +238,6 @@ public static function __callStatic(string $method, array $arguments)
             return $handler->{$method}(...$arguments);
         }
 
-        throw new \BadMethodCallException("Method {$method} does not exist on ".static::class);
+        throw new \BadMethodCallException("Method {$method} does not exist on " . static::class);
     }
 }