Prevent array to string conversion in Subset matcher

CHANGELOG.md

@@ -28,6 +28,7 @@
 * [#1245 Deprecate hamcrest/hamcrest-php package](https://github.com/mockery/mockery/pull/1245)
 * [#1246 Add BUG_REPORT.yml Issue template](https://github.com/mockery/mockery/pull/1246)
 * [#1250 Deprecate PHP <=8.0](https://github.com/mockery/mockery/issues/1250)
+* [#1253 Prevent array to string conversion when serialising a Subset matcher](https://github.com/mockery/mockery/issues/1253)
 
 ## 1.3.6 (2022-09-07)
 * PHP 8.2 | Fix "Use of "parent" in callables is deprecated" notice #1169

library/Mockery/Matcher/Subset.php

@@ -81,12 +81,21 @@ public function match(&$actual)
      */
     public function __toString()
     {
-        $return = '<Subset[';
-        $elements = array();
-        foreach ($this->expected as $k=>$v) {
-            $elements[] = $k . '=' . (string) $v;
+        return '<Subset' . $this->formatArray($this->expected) . ">";
+    }
+
+    /**
+     * Recursively format an array into the string representation for this matcher
+     *
+     * @param array $array
+     * @return string
+     */
+    protected function formatArray(array $array)
+    {
+        $elements = [];
+        foreach ($array as $k => $v) {
+            $elements[] = $k . '=' . (is_array($v) ? $this->formatArray($v) : (string) $v);
         }
-        $return .= implode(', ', $elements) . ']>';
-        return $return;
+        return "[" . implode(", ", $elements) . "]";
     }
 }

tests/Mockery/Matcher/SubsetTest.php

@@ -94,4 +94,28 @@ public function it_returns_false_if_actual_is_not_an_array()
 
         $this->assertFalse($matcher->match($actual));
     }
+
+    /** @test */
+    public function it_correctly_formats_nested_arrays_into_a_string()
+    {
+        $expected = [
+            "foo" => 123,
+            "bar" => [
+                "baz" => 456
+            ]
+        ];
+
+        $matcher = new Subset($expected);
+        $actual = $matcher->__toString();
+
+        $tests = [
+            "/foo=123/",
+            "/bar=\\[[^[\\]]+\\]/", // e.g. bar=[<anything other than square brackets>]
+            "/baz=456/"
+        ];
+
+        foreach ($tests as $pattern) {
+            $this->assertMatchesRegularExpression($pattern, $actual);
+        }
+    }
 }