Add rule for countable

src/Rules/PHPUnit/AssertSameWithCountRule.php

@@ -4,6 +4,7 @@
 
 use PhpParser\Node;
 use PHPStan\Analyser\Scope;
+use PHPStan\Type\ObjectType;
 
 /**
  * @implements \PHPStan\Rules\Rule<\PhpParser\NodeAbstract>
@@ -44,6 +45,21 @@ public function processNode(Node $node, Scope $scope): array
 			];
 		}
 
+		if (
+			$right instanceof Node\Expr\MethodCall
+			&& $right->name instanceof Node\Identifier
+			&& strtolower($right->name->toString()) === 'count'
+			&& count($right->args) === 0
+		) {
+			$type = $scope->getType($right->var);
+
+			if ((new ObjectType(\Countable::class))->isSuperTypeOf($type)->yes()) {
+				return [
+					'You should use assertCount($expectedCount, $variable) instead of assertSame($expectedCount, $variable->count()).',
+				];
+			}
+		}
+
 		return [];
 	}
 

tests/Rules/PHPUnit/AssertSameWithCountRuleTest.php

@@ -24,7 +24,11 @@ public function testRule(): void
 			],
 			[
 				'You should use assertCount($expectedCount, $variable) instead of assertSame($expectedCount, count($variable)).',
-				20,
+				22,
+			],
+			[
+				'You should use assertCount($expectedCount, $variable) instead of assertSame($expectedCount, $variable->count()).',
+				30,
 			],
 		]);
 	}

tests/Rules/PHPUnit/data/assert-same-count.php

@@ -12,12 +12,29 @@ public function testAssertSameWithCount()
 
 	public function testAssertSameWithCountMethodIsOK()
 	{
-		$this->assertSame(5, $this->count()); // OK
+		$foo = new \stdClass();
+
+		$this->assertSame(5, $foo->count()); // OK
 	}
 
 	public function testAssertSameIsDetectedWithDirectAssertAccess()
 	{
 		\PHPUnit\Framework\Assert::assertSame(5, count([1, 2, 3]));
 	}
 
+	public function testAssertSameWithCountMethodForCountableVariableIsNotOK()
+	{
+		$foo = new \stdClass();
+		$foo->bar = new Bar ();
+
+		$this->assertSame(5, $foo->bar->count());
+	}
+
 }
+
+class Bar implements \Countable {
+	public function count()
+	{
+		return 1;
+	}
+};