AssertSameNullExpectedRule

Author: mhujer

README.md

@@ -18,6 +18,10 @@ It also contains this framework-specific rule (can be enabled separately):
 
 * Check that both values passed to `assertSame()` method are of the same type.
 
+It also contains this strict framework-specific rule (can be enabled separately):
+
+* Check that you are not using `assertSame()` with `null` as expected value. `assertNull()` should be used instead.
+
 ## How to document mock objects in phpDocs?
 
 If you need to configure the mock even after you assign it to a property or return it from a method, you should add `PHPUnit_Framework_MockObject_MockObject` to the phpDoc:
@@ -81,3 +85,9 @@ To perform framework-specific checks, include also this file:
 ```
 	- vendor/phpstan/phpstan-phpunit/rules.neon
 ```
+
+To perform addition strict PHPUnit checks, include also this file:
+
+```
+	- vendor/phpstan/phpstan-phpunit/strictRules.neon
+```

src/Rules/PHPUnit/AssertSameNullExpectedRule.php

@@ -0,0 +1,46 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\PHPUnit;
+
+use PhpParser\Node;
+use PHPStan\Analyser\Scope;
+use PHPStan\Type\NullType;
+
+class AssertSameNullExpectedRule implements \PHPStan\Rules\Rule
+{
+
+	public function getNodeType(): string
+	{
+		return \PhpParser\NodeAbstract::class;
+	}
+
+	/**
+	 * @param \PhpParser\Node\Expr\MethodCall|\PhpParser\Node\Expr\StaticCall $node
+	 * @param \PHPStan\Analyser\Scope $scope
+	 * @return string[] errors
+	 */
+	public function processNode(Node $node, Scope $scope): array
+	{
+		if (!AssertRuleHelper::isMethodOrStaticCallOnTestCase($node, $scope)) {
+			return [];
+		}
+
+		if (count($node->args) < 2) {
+			return [];
+		}
+		if (!is_string($node->name) || strtolower($node->name) !== 'assertsame') {
+			return [];
+		}
+
+		$leftType = $scope->getType($node->args[0]->value);
+
+		if ($leftType instanceof NullType) {
+			return [
+				'You should use assertNull() instead of assertSame(null, $actual).',
+			];
+		}
+
+		return [];
+	}
+
+}

strictRules.neon

@@ -0,0 +1,5 @@
+services:
+	-
+		class: PHPStan\Rules\PHPUnit\AssertSameNullExpectedRule
+		tags:
+			- phpstan.rules.rule

tests/Rules/PHPUnit/AssertSameNullExpectedRuleTest.php

@@ -0,0 +1,29 @@
+<?php declare(strict_types = 1);
+
+namespace PHPStan\Rules\PHPUnit;
+
+use PHPStan\Rules\Rule;
+
+class AssertSameNullExpectedRuleTest extends \PHPStan\Testing\RuleTestCase
+{
+
+	protected function getRule(): Rule
+	{
+		return new AssertSameNullExpectedRule();
+	}
+
+	public function testRule()
+	{
+		$this->analyse([__DIR__ . '/data/assert-same-null-expected.php'], [
+			[
+				'You should use assertNull() instead of assertSame(null, $actual).',
+				10,
+			],
+			[
+				'You should use assertNull() instead of assertSame(null, $actual).',
+				13,
+			],
+		]);
+	}
+
+}

tests/Rules/PHPUnit/data/assert-same-null-expected.php

@@ -0,0 +1,22 @@
+<?php declare(strict_types = 1);
+
+namespace ExampleTestCase;
+
+class AssertSameNullExpectedTestCase extends \PHPUnit\Framework\TestCase
+{
+
+	public function testAssertSameWithNullAsExpected()
+	{
+		$this->assertSame(null, 'a');
+
+		$a = null;
+		$this->assertSame($a, 'b');
+
+		$this->assertSame('a', 'b'); // OK
+
+		/** @var string|null $c */
+		$c = null;
+		$this->assertSame($c, 'foo'); // nullable is OK
+	}
+
+}