Send alerts for all space launch test flights

In addition to the configured FOLLOW_LAUNCHES, also send emails for any
launch whose mission.type == "Test Flight" even if its slug is not in
FOLLOW_LAUNCHES.

Fixes #192.

update.py

@@ -239,6 +239,12 @@ View all launches: https://edwardbetts.com/agenda/launches
     agenda.mail.send_mail(config, subject, body)
 
 
+def is_test_flight(launch: StrDict) -> bool:
+    """Return True if the launch is a test flight."""
+    mission = typing.cast(dict[str, typing.Any] | None, launch.get("mission"))
+    return bool(mission and mission.get("type") == "Test Flight")
+
+
 def get_launch_by_slug(data: StrDict, slug: str) -> StrDict | None:
     """Find last update for space launch."""
     return {item["slug"]: typing.cast(StrDict, item) for item in data["results"]}.get(
@@ -247,29 +253,58 @@ def get_launch_by_slug(data: StrDict, slug: str) -> StrDict | None:
 
 
 def update_thespacedevs(config: flask.config.Config) -> None:
-    """Update cache of space launch API."""
+    """Update cache of space launch API and send emails on relevant changes.
+
+    In addition to the configured FOLLOW_LAUNCHES, also send emails for any
+    launch whose mission.type == "Test Flight" even if its slug is not in
+    FOLLOW_LAUNCHES.
+    """
     rocket_dir = os.path.join(config["DATA_DIR"], "thespacedevs")
 
     existing_data = agenda.thespacedevs.load_cached_launches(rocket_dir)
     assert existing_data
-    prev_launches = {
-        slug: get_launch_by_slug(existing_data, slug)
-        for slug in config["FOLLOW_LAUNCHES"]
+
+    # Always follow configured slugs
+    follow_slugs: set[str] = set(config["FOLLOW_LAUNCHES"])
+
+    # Identify test-flight slugs present in the previous cache
+    prev_test_slugs: set[str] = {
+        typing.cast(str, item["slug"])
+        for item in existing_data.get("results", [])
+        if is_test_flight(typing.cast(StrDict, item))
     }
 
     t0 = time()
     data = agenda.thespacedevs.next_launch_api_data(rocket_dir)
     if not data:
         return  # thespacedevs API call failed
-    cur_launches = {
-        slug: get_launch_by_slug(data, slug) for slug in config["FOLLOW_LAUNCHES"]
+
+    # Identify test-flight slugs present in the current data
+    cur_test_slugs: set[str] = {
+        typing.cast(str, item["slug"])
+        for item in data.get("results", [])
+        if is_test_flight(typing.cast(StrDict, item))
     }
 
-    for slug in config["FOLLOW_LAUNCHES"]:
-        prev, cur = prev_launches[slug], cur_launches[slug]
+    # Add any test-flight slugs (whether old or new), excluding those we already
+    # explicitly follow.
+    extra_test_slugs = (prev_test_slugs | cur_test_slugs) - follow_slugs
+
+    # Final set of slugs to evaluate for changes
+    slugs_to_check = follow_slugs | extra_test_slugs
+
+    # Build prev/cur lookup dicts for all slugs we're checking
+    prev_launches = {
+        slug: get_launch_by_slug(existing_data, slug) for slug in slugs_to_check
+    }
+    cur_launches = {slug: get_launch_by_slug(data, slug) for slug in slugs_to_check}
+
+    # Emit reports when a launch appears/disappears or changes
+    for slug in slugs_to_check:
+        prev, cur = prev_launches.get(slug), cur_launches.get(slug)
         if prev is None and cur is None:
             continue
-        if prev and cur and prev["last_updated"] == cur["last_updated"]:
+        if prev and cur and prev.get("last_updated") == cur.get("last_updated"):
             continue
         report_space_launch_change(config, prev, cur)