Add initial integration tests for the Client class

Unfortunately, one of the two tests is just an example of what we would
expect to work later: We cannot post incidents to Argus as the admin
user, we have to create a source system and a user/token combo for that
source system first.

tests/test_client.py

@@ -0,0 +1,35 @@
+from collections.abc import Iterable
+from datetime import datetime
+
+import pytest
+
+from pyargus.client import Client
+from pyargus.models import Incident
+
+
+class TestApiIntegration:
+    def test_incidents_list_should_return_iterable(self, api_client):
+        incidents = api_client.get_incidents()
+        assert isinstance(incidents, Iterable)
+
+    @pytest.mark.xfail(
+        reason="We must add a source system to Argus to do this properly"
+    )
+    def test_when_posting_incident_it_should_return_full_incident(self, api_client):
+        post = Incident(
+            description="The earth was demolished to make way for a hyperspace bypass",
+            start_time=datetime.now(),
+            tags={
+                "host": "earth.example.org",
+            },
+        )
+        result = api_client.post_incident(post)
+        assert isinstance(result, Incident)
+        assert result.description == post.description
+        assert result.pk
+
+
+@pytest.fixture
+def api_client(argus_api):
+    url, token = argus_api
+    return Client(url, token)