tests: Add tests for communities and collections

Also, separate tests for items, communities, and collections into
their own files, leaving a single test for docs in its own file.

tests/test_api_docs.py

@@ -0,0 +1,18 @@
+from falcon import testing
+import pytest
+
+from dspace_statistics_api.app import api
+
+
+@pytest.fixture
+def client():
+    return testing.TestClient(api)
+
+
+def test_get_docs(client):
+    """Test requesting the documentation at the root."""
+
+    response = client.simulate_get("/")
+
+    assert isinstance(response.content, bytes)
+    assert response.status_code == 200