Added ExceptionInterface as marker for package-specific exceptions

docs/book/migration.md

@@ -81,6 +81,9 @@ If you wish to use those types, you will need to decorate them in a
   only operate on the response returned by `$next`, or produce a concrete
   response yourself.
 
+- `Zend\Stratigility\Exception\ExceptionInterface` - marker for
+  package-specific exceptions.
+
 ### Removed classes and exceptions
 
 The following classes have been removed:

src/Exception/ExceptionInterface.php

@@ -0,0 +1,15 @@
+<?php
+/**
+ * @see       https://github.com/zendframework/zend-stratigility for the canonical source repository
+ * @copyright Copyright (c) 2017 Zend Technologies USA Inc. (https://www.zend.com)
+ * @license   https://github.com/zendframework/zend-stratigility/blob/master/LICENSE.md New BSD License
+ */
+
+namespace Zend\Stratigility\Exception;
+
+/**
+ * Marker interface for package-specific exceptions.
+ */
+interface ExceptionInterface
+{
+}

src/Exception/InvalidMiddlewareException.php

@@ -10,7 +10,7 @@
 use Interop\Http\Server\MiddlewareInterface;
 use InvalidArgumentException;
 
-class InvalidMiddlewareException extends InvalidArgumentException
+class InvalidMiddlewareException extends InvalidArgumentException implements ExceptionInterface
 {
     /**
      * Create and return an InvalidArgumentException detailing the invalid middleware type.

src/Exception/MissingResponseException.php

@@ -13,7 +13,7 @@
  * Exception thrown when the internal stack of Zend\Stratigility\Next is
  * exhausted, but no response returned.
  */
-class MissingResponseException extends OutOfBoundsException
+class MissingResponseException extends OutOfBoundsException implements ExceptionInterface
 {
     public static function forCallableMiddleware(callable $middleware) : self
     {

src/Exception/MissingResponsePrototypeException.php

@@ -14,7 +14,7 @@
  * Exception thrown by the DoublePassMiddlewareWrapper when no response
  * prototype is provided, and Diactoros is not available to create a default.
  */
-class MissingResponsePrototypeException extends UnexpectedValueException
+class MissingResponsePrototypeException extends UnexpectedValueException implements ExceptionInterface
 {
     public static function create() : self
     {

test/Exception/ExceptionTest.php

@@ -0,0 +1,36 @@
+<?php
+/**
+ * @see       https://github.com/zendframework/zend-stratigility for the canonical source repository
+ * @copyright Copyright (c) 2017 Zend Technologies USA Inc. (https://www.zend.com)
+ * @license   https://github.com/zendframework/zend-stratigility/blob/master/LICENSE.md New BSD License
+ */
+
+namespace ZendTest\Stratigility\Exception;
+
+use Generator;
+use PHPUnit\Framework\TestCase;
+use Zend\Stratigility\Exception\ExceptionInterface;
+
+class ExceptionTest extends TestCase
+{
+    public function exception() : Generator
+    {
+        $namespace = substr(ExceptionInterface::class, 0, strrpos(ExceptionInterface::class, '\\') + 1);
+
+        $exceptions = glob(__DIR__ . '/../../src/Exception/*.php');
+        foreach ($exceptions as $exception) {
+            $class = substr(basename($exception), 0, -4);
+
+            yield $class => [$namespace . $class];
+        }
+    }
+
+    /**
+     * @dataProvider exception
+     */
+    public function testExceptionIsInstanceOfExceptionInterface(string $exception) : void
+    {
+        self::assertContains('Exception', $exception);
+        self::assertTrue(is_a($exception, ExceptionInterface::class, true));
+    }
+}