public void TestRemoveRelation()
{
Relation testRelation = new Relation();
testRelation.Id = -1;
var source = new MemoryDataSource();
source.AddRelation(testRelation);
// test if the relation is actually there.
Assert.AreEqual(testRelation, source.GetRelation(-1));
// remove the relation.
source.RemoveRelation(-1);
// test if the relation is actually gone.
Assert.IsNull(source.GetRelation(-1));
}