public void testDifference()
{
Graph g1 = graphWith( "x R y; p R q" );
Graph g2 = graphWith( "r A s; x R y" );
Difference d = new Difference( g1, g2 );
assertOmits( "Difference", d, "x R y" );
assertContains( "Difference", "p R q", d );
assertOmits( "Difference", d, "r A s" );
if (d.size() != 1)
fail( "oops: size of difference is not 1" );
d.add( triple( "cats eat cheese" ) );
assertContains( "Difference.L", "cats eat cheese", g1 );
assertOmits( "Difference.R", g2, "cats eat cheese" );
}