add more tests

Author: staabm

tests/PHPStan/Rules/Comparison/ImpossibleCheckTypeFunctionCallRuleTest.php

@@ -1083,6 +1083,14 @@ public function testBug12087c(): void
 				17,
 				$tipText,
 			],
+			[
+				'Call to function is_null() with 10 will always evaluate to false.',
+				23,
+			],
+			[
+				'Call to function is_null() with null will always evaluate to true.',
+				29,
+			],
 		]);
 	}
 

tests/PHPStan/Rules/Comparison/data/bug-12087c.php

@@ -16,3 +16,16 @@ function doFoo()
 
 	is_null($value = $foo = Button::tryFrom($value));
 }
+
+function doFoo2() {
+	$value = 10;
+
+	is_null($value ??= Button::tryFrom($value));
+}
+
+function doFoo3() {
+	$value = null;
+
+	is_null($value ??= Button::tryFrom($value));
+}
+