An object that is a boolean will either have a class of TrueClass or FalseClass so the following one-liner should do the trick
mybool = true
mybool.class == TrueClass || mybool.class == FalseClass
=> true
The following would also give you true/false boolean type check result
mybool = true
[TrueClass, FalseClass].include?(mybool.class)
=> true