ISampleConstraint: 'getExpectedVariables' returns value that is ignored in jUnit tests
JUnit test case classes that implement ISampleConstraint interface should implement
getExpectedVariables method. In fact, this method's returned value is ignored everwhere.
Probably we should either to made our tests more solver-specific (AFAIK, this problem comes from the fact that Z3 and CVC4 solvers return different values on same constraints), or change this method somehow.