See also:
In this guide we will see how to test charm code that interacts with Juju relations.
Suppose that we are writing tests for a charm that copies data provided to it via a “foo” relation to its unit databag:
class MyCharm(CharmBase):
...
def _on_foo_relation_changed(self, e):
rel = e.relation
rel.data[self.unit]['data'] = rel.data[e.app]['data']
Now we write a scenario test validating this behaviour. We import MyCharm and a few objects from scenario:
from charm import MyCharm
from scenario import Relation, State, Context
Then the test code:
def test_relation_data_copied():
# IF the remote end has provided data "baz"
relation = Relation(
endpoint="foo",
remote_app_data={"data": "baz"},
)
state_in = State(relations=[relation])
# WHEN a foo_relation_changed is fired on MyCharm
ctx = Context(MyCharm,
meta={"name": "foo"})
state_out = ctx.run(relation.relation_changed_event, state_in)
# THEN the charm has copied the remote-provided data to its local unit databag
assert state_out.relations[0].local_unit_data == {"data": "baz"}