This block could be updated to use `containsKeys` from assertj [containsKeys documentation](http://joel-costigliola.github.io/assertj/core/api/org/assertj/core/api/AbstractMapAssert.html#containsKeys(K...))

I haven't found a method to avoid the additional size check, unfortunately. It might be good to move the size check after the other checks, since it will usually be more useful to see specifically what is missing rather than just that something is missing.