test/api: add checks for the api infrastructure

Add a check for `api.BaseAPI` by implementing a test API and test
that receiving messages and dispatching them works as planned.

test/mod/test_api.py

@@ -0,0 +1,66 @@
+#
+# Test for API infrastructure
+#
+
+import os
+import tempfile
+import unittest
+
+import osbuild
+from osbuild.util import jsoncomm
+
+
+class APITester(osbuild.api.BaseAPI):
+    """Records the number of messages and if it got cleaned up"""
+    def __init__(self, sockaddr):
+        super().__init__(sockaddr)
+        self.clean = False
+        self.messages = 0
+
+    def _dispatch(self, server):
+        msg, _, addr = server.recv()
+        self.messages += 1
+
+        if msg["method"] == "echo":
+            msg["method"] = "reply"
+            server.send(msg, destination=addr)
+
+    def _cleanup(self):
+        self.clean = True
+
+
+class TestAPI(unittest.TestCase):
+    """Check API infrastructure"""
+    def setUp(self):
+        self.tmp = tempfile.TemporaryDirectory()
+
+    def tearDown(self):
+        self.tmp.cleanup()
+
+    def test_basic(self):
+        # Basic API communication and cleanup checks
+
+        socket = os.path.join(self.tmp.name, "socket")
+        api = APITester(socket)
+        with api:
+            with jsoncomm.Socket.new_client(socket) as client:
+                req = {'method': 'echo', 'data': 'Hello'}
+                client.send(req)
+                msg, _, _ = client.recv()
+                self.assertEqual(msg["method"], "reply")
+                self.assertEqual(req["data"], msg["data"])
+
+        self.assertEqual(api.clean, True)
+        self.assertEqual(api.messages, 1)
+
+        # Assert proper cleanup
+        self.assertIsNone(api.thread)
+        self.assertIsNone(api.event_loop)
+
+    def test_reentrancy_guard(self):
+        socket = os.path.join(self.tmp.name, "socket")
+        api = APITester(socket)
+        with api:
+            with self.assertRaises(AssertionError):
+                with api:
+                    pass