Fix serialization of ComparisionFailure with PDO in stacktrace.

src/ComparisonFailure.php

@@ -15,7 +15,7 @@
 /**
  * Thrown when an assertion for string equality failed.
  */
-class ComparisonFailure extends \RuntimeException
+class ComparisonFailure extends \RuntimeException implements \Serializable
 {
     /**
      * Expected value of the retrieval which does not match $actual.
@@ -125,4 +125,26 @@ public function toString()
     {
         return $this->message . $this->getDiff();
     }
+
+    /**
+     * Serialises all parts of the comparison failure, apart from the stacktrace which might contain references to
+     * objects which cannot be serialised.
+     *
+     * @return string
+     */
+    public function serialize()
+    {
+        return serialize(array(
+            $this->expected, $this->actual, $this->expectedAsString, $this->actualAsString,
+            $this->identical, $this->message, $this->file, $this->line
+        ));
+    }
+
+    public function unserialize($serialized)
+    {
+        list(
+            $this->expected, $this->actual, $this->expectedAsString, $this->actualAsString,
+            $this->identical, $this->message, $this->file, $this->line
+        ) = unserialize($serialized);
+    }
 }

tests/ComparisonFailureTest.php

@@ -56,4 +56,24 @@ public function testDiffNotPossible(): void
         $this->assertSame('', $failure->getDiff());
         $this->assertSame('test', $failure->toString());
     }
+
+    public function testSerializesWithoutStackTrace()
+    {
+        $instance = new NonSerializableClass;
+
+        $failure = $this->functionWithNonSerializableParam($instance);
+
+        $serialised = serialize($failure);
+        $deserialised = unserialize($serialised);
+
+        $this->assertSame($failure->getActual(), $deserialised->getActual());
+        $this->assertSame($failure->getExpected(), $deserialised->getExpected());
+        $this->assertSame($failure->getActualAsString(), $deserialised->getActualAsString());
+        $this->assertSame($failure->getExpectedAsString(), $deserialised->getExpectedAsString());
+        $this->assertSame($failure->toString(), $deserialised->toString());
+    }
+
+    private function functionWithNonSerializableParam(NonSerializableClass $instance) {
+        return new ComparisonFailure('a', 'b', 'a', 'b', false, 'test');
+    }
 }

tests/_fixture/NonSerializableClass.php

@@ -0,0 +1,20 @@
+<?php
+/*
+ * This file is part of sebastian/comparator.
+ *
+ * (c) Sebastian Bergmann <[email protected]>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace SebastianBergmann\Comparator;
+
+class NonSerializableClass implements \Serializable {
+    public function serialize()
+    {
+        throw new \Error('This class cannot be serialized');
+    }
+
+    public function unserialize($serialized) {}
+}