--- /dev/null
+<?php
+/*
+ * This file is part of PHPUnit.
+ *
+ * (c) Sebastian Bergmann <sebastian@phpunit.de>
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+/**
+ * Constraint that asserts that a string is valid JSON.
+ *
+ * @since Class available since Release 3.7.20
+ */
+class PHPUnit_Framework_Constraint_IsJson extends PHPUnit_Framework_Constraint
+{
+ /**
+ * Evaluates the constraint for parameter $other. Returns true if the
+ * constraint is met, false otherwise.
+ *
+ * @param mixed $other Value or object to evaluate.
+ *
+ * @return bool
+ */
+ protected function matches($other)
+ {
+ json_decode($other);
+ if (json_last_error()) {
+ return false;
+ }
+
+ return true;
+ }
+
+ /**
+ * Returns the description of the failure
+ *
+ * The beginning of failure messages is "Failed asserting that" in most
+ * cases. This method should return the second part of that sentence.
+ *
+ * @param mixed $other Evaluated value or object.
+ *
+ * @return string
+ */
+ protected function failureDescription($other)
+ {
+ json_decode($other);
+ $error = PHPUnit_Framework_Constraint_JsonMatches_ErrorMessageProvider::determineJsonError(
+ json_last_error()
+ );
+
+ return sprintf(
+ '%s is valid JSON (%s)',
+ $this->exporter->shortenedExport($other),
+ $error
+ );
+ }
+
+ /**
+ * Returns a string representation of the constraint.
+ *
+ * @return string
+ */
+ public function toString()
+ {
+ return 'is valid JSON';
+ }
+}