Android NoSuchMethod issue

I'm writing some tests and I'm getting an issue:

java.lang.NoSuchMethodError: No virtual method primeId(Ljava/lang/String;)/boardingpass/BoardingPass$Builder;

I think it's from Proguard. I'm not sure how to make it work. In my proguard file I said:

-keep class com.boardingpass.BoardingPass { *; }
-keepclassmembers class com.boardingpass.BoardingPass.Builder { *; }

I thought that would keep the methods in, as I think what's happening is that the primeId in the builder is only used here so Proguard might strip it out?

Appreciate any help with it