Better exception message when we do not find candidates

src/ClassDiscovery.php

@@ -4,6 +4,7 @@
 
 use Http\Discovery\Exception\ClassInstantiationFailedException;
 use Http\Discovery\Exception\DiscoveryFailedException;
+use Http\Discovery\Exception\NoCandidateFoundException;
 use Http\Discovery\Exception\StrategyUnavailableException;
 
 /**
@@ -70,6 +71,8 @@ protected static function findOneByType($type)
 
                 return $candidate['class'];
             }
+
+            $exceptions[] = new NoCandidateFoundException($strategy, $candidates);
         }
 
         throw DiscoveryFailedException::create($exceptions);

src/Exception/NoCandidateFoundException.php

@@ -0,0 +1,37 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Http\Discovery\Exception;
+
+use Http\Discovery\Exception;
+
+/**
+ * When we have used a strategy but no candidates provided by that strategy could be used.
+ *
+ * @author Tobias Nyholm <[email protected]>
+ */
+final class NoCandidateFoundException extends \Exception implements Exception
+{
+    /**
+     * @param string $strategy
+     * @param array  $candidates
+     */
+    public function __construct($strategy, array $candidates)
+    {
+        $classes = array_map(
+            function ($a) {
+                return $a['class'];
+            },
+            $candidates
+        );
+
+        $message = sprintf(
+            'No valid candidate found using strategy "%s". We tested the following candidates: %s.',
+            $strategy,
+            implode(', ', $classes)
+        );
+
+        parent::__construct($message);
+    }
+}