Method json() to parse JSON strings

- Parse a JSON string into array
- Test

tests/Features/Expect/json.php

@@ -0,0 +1,14 @@
+<?php
+
+use PHPUnit\Framework\ExpectationFailedException;
+
+test('it properly parses json string', function () {
+    expect('{"name":"Nuno"}')
+        ->json()
+        ->name
+        ->toBe('Nuno');
+});
+
+test('fails with broken json string', function () {
+    expect('{":"Nuno"}')->json();
+})->throws(ExpectationFailedException::class);