Add tests

Author: VincentLanglet

tests/PHPStan/Analyser/nsrt/bug-12312.php

@@ -14,6 +14,9 @@ public function sayLowercase(string $s): void
 		if ($s != '') {
 			assertType('lowercase-string&non-empty-string', $s);
 		}
+		if ('' != $s) {
+			assertType('lowercase-string&non-empty-string', $s);
+		}
 		assertType('lowercase-string', $s);
 	}
 
@@ -25,6 +28,9 @@ public function sayUppercase(string $s): void
 		if ($s != '') {
 			assertType('non-empty-string&uppercase-string', $s);
 		}
+		if ('' != $s) {
+			assertType('non-empty-string&uppercase-string', $s);
+		}
 		assertType('uppercase-string', $s);
 	}
 
@@ -36,6 +42,9 @@ public function sayBoth(string $s): void
 		if ($s != '') {
 			assertType('lowercase-string&non-empty-string&uppercase-string', $s);
 		}
+		if ('' != $s) {
+			assertType('lowercase-string&non-empty-string&uppercase-string', $s);
+		}
 		assertType('lowercase-string&uppercase-string', $s);
 	}
 }