This PHPUnit constraint class is for applying another constraint to a value inside a nested array structure.

NestedArrayConstraint.php

<?php
/**
 * This constraint class is for applying another constraint to a value inside a nested array structure.
 *
 * When initializing this constraint you specify a "key path" - an array of keys, each accessing the next level of the
 * array to check.
 *
 * @author Gabriel Birke <[email protected]>
 */
class NestedArrayConstraint extends PHPUnit_Framework_Constraint
{

    private $path;
    private $constraint;
    private $pathMatches = false;
    private $pathValue;

    /**
     * @param array $path Key path to the desired value
     * @param PHPUnit_Framework_Constraint $constraint Constraint that will be evaluated with the value at the end of the key path
     */
    public function __construct($path, PHPUnit_Framework_Constraint $constraint){
        $this->path = $path;
        $this->constraint = $constraint;
    }

    /**
     * Check if the array contains the keys in $this->path and if it does, delegate evaluation to internal constraint
     *
     * @param mixed $other
     * @param string $description
     * @param bool $returnResult
     * @return bool|mixed
     */
    public function evaluate($other, $description = '', $returnResult = FALSE)
    {
        $success = false;

        if($this->matches($other) && $this->constraint->evaluate($this->pathValue, $description, TRUE)) {
            $success = true;
        }

        if ($returnResult) {
            return $success;
        }

        if (!$success) {
            $this->fail($other, $description);
        }
    }

    /**
     * Check if $other is an array and contains all the keys specified in $this->path
     *
     * @param mixed $other
     * @return bool
     */
    protected function matches($other)
    {
        if(!is_array($other)) {
            return false;
        }
        $pointer = $other;
        foreach($this->path as $p) {
            if(!isset($pointer[$p])) {
                return false;
            }
            $pointer = $pointer[$p];
        }
        $this->pathMatches = true;
        $this->pathValue = $pointer;
        return true;
    }

    /**
     * Depending on the type of failure, choose different values for $other
     *
     * @param mixed $other
     * @param string $description
     * @param PHPUnit_Framework_ComparisonFailure $comparisonFailure
     */
    protected function fail($other, $description, PHPUnit_Framework_ComparisonFailure $comparisonFailure = NULL)
    {
        if($this->pathMatches) {
            parent::fail($this->pathValue, $description, $comparisonFailure);
        }
        else {
            parent::fail($other, $description, $comparisonFailure);
        }

    }

    /**
     * Returns a string representation of the object.
     *
     * @return string
     */
    public function toString()
    {
        if($this->pathMatches) {
            return $this->constraint->toString();
        }
        else {
            $keys = implode('', array_map(function($v){ return "[$v]"; }, $this->path));
            return "has nested key path ". $keys;
        }
    }
}