def test_cluster_division_separates_cluster_with_unrelated_items(scotland, alba, england, goat):
cluster_scotland = Cluster()
cluster_scotland.save()
cluster_england_and_goat = Cluster()
cluster_england_and_goat.save()
scotland.cluster = cluster_scotland
scotland.save()
alba.cluster = cluster_scotland
alba.save()
england.cluster = cluster_england_and_goat
england.save()
goat.cluster = cluster_england_and_goat
goat.save()
Cluster.clear_empty()
assert Cluster.objects.count() == 2
Cluster.divide()
# Django won't notice the clusters changing unless we re-read fields
scotland.refresh_from_db()
england.refresh_from_db()
goat.refresh_from_db()
# We expect one cluster to divide, so our original 2 are now 3
assert Cluster.objects.count() == 3
# Scotland cluster untouched as it has two identical items
assert len(cluster_scotland) == 2
# England and Goat should be in their own clusters as they are unrelated
assert england.cluster != goat.cluster
def test_cluster_cohesion_is_one_when_items_are_identical(scotland, alba):
cluster = Cluster()
cluster.save()
scotland.cluster = cluster
alba.cluster = cluster
assert cluster.cohesion == 1.0
def test_cluster_cohesion_is_zero_when_items_are_fully_unrelated(scotland, goat):
cluster = Cluster()
cluster.save()
scotland.cluster = cluster
scotland.save()
goat.cluster = cluster
goat.save()
assert cluster.cohesion == 0.0
def test_cluster_cohesion_is_between_zero_and_one_when_items_overlaps(scotland, england):
cluster = Cluster()
cluster.save()
scotland.cluster = cluster
scotland.save()
england.cluster = cluster
england.save()
# Hard-coded to test for the particular method in use, but theoretically
# the test should probably just check that it's strictly between 0 and 1.
assert round(cluster.cohesion, 2) == 0.33
def test_agglomerate_merges_two_nearest_clusters(scotland, england, goat):
# Given we have 3 singleton clusters at the start
assert Cluster.objects.all().count() == 3
Cluster.agglomerate()
# Django will have cached these, so refresh to see latest memberships
scotland.refresh_from_db()
england.refresh_from_db()
goat.refresh_from_db()
# we should have lost a cluster
assert Cluster.objects.all().count() == 2
# Check the goat is still in its own singleton cluster
assert goat.cluster.item_set.count() == 1
# England and Scotland should have been merged
assert scotland.cluster == england.cluster
