[backups] Fix pg_dump not found in celery backup task

tests/scrobbles_tests/test_backup_database.py

@@ -5,6 +5,27 @@ import time_machine
 from scrobbles import tasks as scrobbles_tasks
 
 
+def test_locate_pg_dump_returns_which_result(monkeypatch):
+    monkeypatch.setattr(
+        scrobbles_tasks.shutil, "which", lambda name: "/usr/local/bin/pg_dump"
+    )
+    assert scrobbles_tasks._locate_pg_dump() == "/usr/local/bin/pg_dump"
+
+
+def test_locate_pg_dump_falls_back_to_common_locations(monkeypatch):
+    monkeypatch.setattr(scrobbles_tasks.shutil, "which", lambda name: None)
+    monkeypatch.setattr(
+        scrobbles_tasks.glob, "glob", lambda pattern: ["/usr/local/bin/pg_dump"]
+    )
+    assert scrobbles_tasks._locate_pg_dump() == "/usr/local/bin/pg_dump"
+
+
+def test_locate_pg_dump_returns_none_when_unfindable(monkeypatch):
+    monkeypatch.setattr(scrobbles_tasks.shutil, "which", lambda name: None)
+    monkeypatch.setattr(scrobbles_tasks.glob, "glob", lambda pattern: [])
+    assert scrobbles_tasks._locate_pg_dump() is None
+
+
 class FakeWebDAVClient:
     def __init__(self, files=None):
         self.files = files if files is not None else {}