add more corner-case tests for coordinatesAt()
add more corner-case tests for coordinatesAt()

tucnak/marble,tucnak/marble,probonopd/marble,quannt24/marble,probonopd/marble,tucnak/marble,probonopd/marble,probonopd/marble,quannt24/marble,tzapzoor/marble,tucnak/marble,tucnak/marble,quannt24/marble,tzapzoor/marble,probonopd/marble,probonopd/marble,tzapzoor/marble,tzapzoor/marble,probonopd/marble,tzapzoor/marble,quannt24/marble,quannt24/marble,quannt24/marble,tzapzoor/marble,tzapzoor/marble,tzapzoor/marble,tucnak/marble,tucnak/marble,quannt24/marble