Why body match string in postman is passed even string iss not Exits in response?

Following I put in my test to check if ABC string exists or not.

tests["Body matches string"] = responseBody.has("ABC");

so, test pass as ABC was in response now I wanted to test fail so I check

tests["Body matches string"] = responseBody.has("ABC");
tests["Body matches string"] = responseBody.has("XYZ");

but still test pass, how? and if I only check

tests["Body matches string"] = responseBody.has("XYZ");

then it fails.Strange. Is there any way I can check or assert?

Thanks