Added failling test

tests/PHPStan/Collectors/JsonSerializableTest.php

@@ -0,0 +1,63 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Collectors;
+
+use PhpParser\Node;
+use PhpParser\Node\Stmt\If_;
+use PHPStan\Node\CollectedDataNode;
+use PHPStan\Rules\Rule;
+use PHPStan\Rules\UniversalRule;
+use PHPStan\Testing\RuleTestCase;
+
+/**
+ * @extends RuleTestCase<UniversalRule<CollectedDataNode>>
+ */
+class JsonSerializableTest extends RuleTestCase
+{
+
+	/** @var Collector<If_, array<mixed>> */
+	private Collector $collector;
+
+	public function getRule(): Rule
+	{
+		return new UniversalRule(CollectedDataNode::class, static fn (Node $node): array => []);
+	}
+
+	public function testNotDecodable(): void
+	{
+		$this->collector = new UniversalCollector(
+			If_::class,
+			static fn (If_ $node): array => [$node],
+		);
+
+		$this->analyse([__DIR__ . '/data/json-serializable.php'], [
+			[
+				'Data collected by PHPStan\Collectors\UniversalCollector is not JSON decodable and will not work in parallel analysis.',
+				-1,
+			],
+		]);
+	}
+
+	public function testNotJsonSerializable(): void
+	{
+		$this->collector = new UniversalCollector(
+			If_::class,
+			static fn (If_ $node): array => ["\x61\xb0\x62"], // a invalid utf8 string
+		);
+
+		$this->analyse([__DIR__ . '/data/json-serializable.php'], [
+			[
+				'Data collected by PHPStan\Collectors\UniversalCollector is not JSON serializable.',
+				-1,
+			],
+		]);
+	}
+
+	public function getCollectors(): array
+	{
+		return [
+			$this->collector,
+		];
+	}
+
+}

tests/PHPStan/Collectors/data/json-serializable.php

@@ -0,0 +1,5 @@
+<?php
+
+namespace CollectorJsonSerializable;
+
+if (rand(0,1)) {}