--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/weather_server/logfile_test.py	Sat Sep 28 23:17:21 2019 -0400
@@ -0,0 +1,113 @@
+import contextlib
+import datetime
+import pathlib
+import tempfile
+import unittest
+
+import bson
+import pytz
+
+from . import common
+from . import logfile
+from . import types
+
+
+def ts(n):
+    return datetime.datetime.utcfromtimestamp(n).replace(tzinfo=pytz.UTC)
+
+
+class LoggerTest(unittest.TestCase):
+
+    maxDiff = None
+
+    def setUp(self):
+        super().setUp()
+        self.temp_dir = tempfile.TemporaryDirectory()
+        self.log_path = pathlib.Path(self.temp_dir.name) / 'test.bson'
+
+    def tearDown(self):
+        self.temp_dir.cleanup()
+        super().tearDown()
+
+    def test_empty(self):
+        with contextlib.closing(logfile.Logger(str(self.log_path))) as logger:
+            self.assertEqual(logger.data, ())
+
+    def test_loading(self):
+        with self.log_path.open('wb') as outfile:
+            outfile.write(common.bson_encode(dict(
+                sample_time=ts(123),
+                temp_c=420,
+                rh_pct=69,
+                ingest_time=ts(125),
+            )))
+            outfile.write(b'garbage to ignore')
+        with contextlib.closing(logfile.Logger(str(self.log_path))) as logger:
+            self.assertEqual(
+                logger.data,
+                (types.Reading(ts(123), 420, 69, ts(125)),))
+
+    def test_writing(self):
+        with self.log_path.open('wb') as outfile:
+            outfile.write(common.bson_encode(dict(
+                sample_time=ts(123),
+                temp_c=420,
+                rh_pct=69,
+                ingest_time=ts(125),
+            )))
+        with contextlib.closing(logfile.Logger(str(self.log_path))) as logger:
+            logger.write_rows([
+                types.Reading(ts(100), 999, 666, ts(101)),
+                types.Reading(ts(125), 333, 777, ts(200)),
+            ])
+            self.assertEqual(
+                logger.data,
+                (
+                    types.Reading(ts(123), 420, 69, ts(125)),
+                    types.Reading(ts(125), 333, 777, ts(200)),
+                )
+            )
+
+        self.assertEqual(self.read_bsons(), [
+            dict(
+                sample_time=ts(123),
+                temp_c=420,
+                rh_pct=69,
+                ingest_time=ts(125),
+            ),
+            dict(
+                sample_time=ts(125),
+                temp_c=333,
+                rh_pct=777,
+                ingest_time=ts(200),
+            ),
+        ])
+
+    def test_outside_writes(self):
+        with contextlib.closing(logfile.Logger(str(self.log_path))) as logger:
+            logger.write_rows([
+                types.Reading(ts(100), 999, 666, ts(101)),
+                types.Reading(ts(125), 333, 777, ts(200)),
+            ])
+            with self.log_path.open('ab') as outfile:
+                outfile.write(common.bson_encode(dict(
+                    sample_time=ts(1024),
+                    temp_c=256,
+                    rh_pct=128,
+                    ingest_time=ts(4096),
+                )))
+                outfile.flush()
+            self.assertEqual(logger.data, (
+                types.Reading(ts(100), 999, 666, ts(101)),
+                types.Reading(ts(125), 333, 777, ts(200)),
+                types.Reading(ts(1024), 256, 128, ts(4096)),
+            ))
+
+    def read_bsons(self):
+        with self.log_path.open('rb') as infile:
+            return bson.decode_all(
+                infile.read(), common.BSON_OPTIONS)
+
+
+if __name__ == '__main__':
+    unittest.main()