test: add pytest infrastructure and poll() tests

- Add pytest and pytest-asyncio as optional dev dependencies
- Configure asyncio_mode=auto and pythonpath=[src] in pyproject.toml
- Write three tests at the poll() seam:
  * single-page response publishes all Flights and returns the count
  * paginated response follows link:rel=next and publishes all pages
  * HTTP error from raise_for_status() propagates out of poll()

Tests use injected stub HTTP session and mock Kafka engine;
no real network or broker required.

Closes #4

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

pyproject.toml

@@ -23,6 +23,17 @@ dependencies = [
 [project.scripts]
 schiphol = "src.main:main"
 
+[project.optional-dependencies]
+dev = [
+    "pytest>=8.0",
+    "pytest-asyncio>=0.24",
+]
+
+[tool.pytest.ini_options]
+asyncio_mode = "auto"
+testpaths = ["tests"]
+pythonpath = ["src"]
+
 [build-system]
 requires = ["setuptools>=61.0"]
 build-backend = "setuptools.build_meta"

tests/test_poll.py

@@ -0,0 +1,121 @@
+"""Tests for poll() — the Schiphol API fetch-and-publish sweep."""
+
+import pytest
+import requests
+
+from main import poll
+
+# ---------------------------------------------------------------------------
+# Test doubles
+# ---------------------------------------------------------------------------
+
+
+class _NoOpSpan:
+    def __enter__(self):
+        return self
+
+    def __exit__(self, *args):
+        pass
+
+
+class StubTracer:
+    def start_as_current_span(self, name, attributes=None):
+        return _NoOpSpan()
+
+
+class StubResponse:
+    """Minimal requests.Response lookalike."""
+
+    def __init__(self, flights, *, next_url=None, raise_on_status=False):
+        self._flights = flights
+        self._raise = raise_on_status
+        self.headers = {}
+        if next_url:
+            self.headers["link"] = f'<{next_url}>; rel="next"'
+
+    def raise_for_status(self):
+        if self._raise:
+            raise requests.HTTPError("500 Server Error")
+
+    def json(self):
+        return {"flights": self._flights}
+
+
+class StubSession:
+    """Returns pre-configured StubResponse objects keyed by URL."""
+
+    def __init__(self, responses_by_url: dict):
+        self._responses = responses_by_url
+
+    def get(self, url):
+        return self._responses[url]
+
+
+class MockEngine:
+    """Captures every send() call so tests can assert on Kafka output."""
+
+    def __init__(self):
+        self.sent: list[dict] = []
+
+    async def send(self, topic, *, value, key):
+        self.sent.append({"topic": topic, "value": value, "key": key})
+
+
+class FakeApiSettings:
+    base_url = "https://api.example.com/flights"
+
+
+class FakeKafkaSettings:
+    topic = "flights-test"
+
+
+# ---------------------------------------------------------------------------
+# Tests
+# ---------------------------------------------------------------------------
+
+
+async def test_single_page_publishes_all_flights_and_returns_count():
+    """poll() publishes every Flight on a single-page response and returns the count."""
+    flights = [{"id": "1", "flightName": "KL100"}, {"id": "2", "flightName": "KL200"}]
+    session = StubSession({FakeApiSettings.base_url: StubResponse(flights)})
+    engine = MockEngine()
+
+    count = await poll(session, engine, FakeApiSettings(), FakeKafkaSettings(), StubTracer())
+
+    assert count == 2
+    assert len(engine.sent) == 2
+    published_keys = {msg["key"] for msg in engine.sent}
+    assert published_keys == {"1", "2"}
+
+
+async def test_pagination_publishes_flights_across_all_pages():
+    """poll() follows link: rel="next" headers and publishes Flights from every page."""
+    page1_url = FakeApiSettings.base_url
+    page2_url = "https://api.example.com/flights?page=2"
+
+    page1_flights = [{"id": "A"}, {"id": "B"}]
+    page2_flights = [{"id": "C"}, {"id": "D"}, {"id": "E"}]
+
+    session = StubSession(
+        {
+            page1_url: StubResponse(page1_flights, next_url=page2_url),
+            page2_url: StubResponse(page2_flights),
+        }
+    )
+    engine = MockEngine()
+
+    count = await poll(session, engine, FakeApiSettings(), FakeKafkaSettings(), StubTracer())
+
+    assert count == 5
+    assert len(engine.sent) == 5
+
+
+async def test_http_error_propagates_out_of_poll():
+    """poll() lets HTTP errors from raise_for_status() propagate to the caller."""
+    session = StubSession(
+        {FakeApiSettings.base_url: StubResponse([], raise_on_status=True)}
+    )
+    engine = MockEngine()
+
+    with pytest.raises(requests.HTTPError):
+        await poll(session, engine, FakeApiSettings(), FakeKafkaSettings(), StubTracer())