add two simple scenarios for the REST API

setup.cfg

@@ -109,6 +109,7 @@ dev =
     isort
     mock
     pytest
+    pytest-bdd
     pytest-cov
     pylint
     pytype

tests/features/api.feature

@@ -0,0 +1,15 @@
+Feature: slo-generator API
+    A REST-ful API to interact with the SLO Generator
+
+    Scenario: Calling the API endpoint with a GET
+        Given I am a public, unauthenticated user
+        When I call the API endpoint with a GET
+        Then The API is available
+
+    Scenario: Calling the API endpoint with a POST and an SLO definition
+        Given I am a public, unauthenticated user
+        When I call the API endpoint with a POST and an SLO definition
+        Then The API is available
+        And The API response is not empty
+        And The API response has the expected format
+        And The API response has the expected content

tests/step_defs/test_api.py

@@ -0,0 +1,85 @@
+import pytest
+import requests
+from pytest_bdd import given, scenario, then, when
+
+# The URL of an SLO Generator API running on Cloud Run with the latest version
+API_CLOUD_RUN_URL: str = "https://slo-generator-ulho4vepfq-ew.a.run.app/"
+
+
+class ApiHelper:
+    responseCode = None
+
+
+@pytest.fixture
+def api():
+    helper = ApiHelper()
+    return helper
+
+
+@scenario("../features/api.feature", "Calling the API endpoint with a GET")
+def test_call_api_with_get(api):
+    pass
+
+
+@given("I am a public, unauthenticated user")
+def public_unauthenticated_user():
+    pass
+
+
+@when("I call the API endpoint with a GET")
+def call_api_endpoint_with_get(api: ApiHelper):
+    response = requests.get(API_CLOUD_RUN_URL)
+    api.responseCode = response.status_code
+
+
+@then("The API is available")
+def api_is_available(api: ApiHelper):
+    assert api.responseCode == 200
+
+
+@scenario(
+    "../features/api.feature",
+    "Calling the API endpoint with a POST and an SLO definition",
+)
+def test_call_api_with_post_and_slo_definition(api):
+    pass
+
+
+@when("I call the API endpoint with a POST and an SLO definition")
+def call_api_endpoint_with_post_and_slo_definition(api: ApiHelper):
+    with open("./samples/cloud_monitoring/slo_gae_app_availability.yaml", "rb") as f:
+        payload = f.read()
+        payload = payload.replace(b"${GAE_PROJECT_ID}", b"slo-generator-ci-a2b4")
+        headers = {"content-type": "application/x-www-form-urlencoded"}
+        response = requests.post(API_CLOUD_RUN_URL, data=payload, headers=headers)
+        api.responseCode = response.status_code
+        api.json = response.json()
+
+
+@then("The API response is not empty")
+def api_returns_some_data(api: ApiHelper):
+    assert api.json
+
+
+@then("The API response has the expected format")
+def api_response_has_expected_format(api: ApiHelper):
+    assert len(api.json) == 2 and all(
+        key in api.json[0]
+        for key in (
+            "alert",
+            "backend",
+            "bad_events_count",
+            "good_events_count",
+            "events_count",
+            "error_budget_burn_rate",
+        )
+    )
+
+
+@then("The API response has the expected content")
+def api_response_has_expected_content(api: ApiHelper):
+    assert (
+        api.json[0]["exporters"] == ["cloud_monitoring"]
+        and api.json[0]["bad_events_count"] + api.json[0]["good_events_count"]
+        == api.json[0]["events_count"]
+    )