log_read: Deal with rare case of wrong fstat at test start

diff --git a/src/log_read.py b/src/log_read.py
index c6b646e..52b8cec 100644 (file)
--- a/src/log_read.py
+++ b/src/log_read.py
@@ -225,9 +225,11 @@ class IterativeReader(object):
                              category=LogReadWarning)
                         self.ignore[idx] = True
                 else:
-                    if new_size < last_size:
-                        warn('{0} / {1} has become smaller ({2} --> {3})!'
-                             .format(obj, description, last_size, new_size),
+                    if new_size < last_size:  # happened at start of some tests
+                        warn('{0} / {1} has become smaller ({2} --> {3})! '
+                             .format(obj, description, last_size, new_size)
+                             + 'Maybe you are reading from a half-initialized '
+                             + 'file?',
                              category=LogReadWarning)
                     try:
                         new_data = obj.read()

diff --git a/test/test_log_read.py b/test/test_log_read.py
index daf8ea6..7fd7fac 100644 (file)
--- a/test/test_log_read.py
+++ b/test/test_log_read.py
@@ -29,8 +29,9 @@ from tempfile import mkstemp
 import os
 import time
 import logging
+from warnings import warn
 
-from src.log_read import IterativeReader, LineReader
+from src.log_read import IterativeReader, LineReader, LogReadWarning
 
 # get best clock
 from sys import version_info
@@ -198,12 +199,22 @@ class LogReadTester(unittest.TestCase):
             with open(self.temp_file, 'rt') as file_handle:
                 reader = IterativeReader(file_handle)
                 self.helper_test_len(reader, 1)
-                for counter, (desc, text) in enumerate(reader):
+                counter = -1        # we may have to adapt this manually
+                for desc, text in reader:
                     receive_time = perf_counter()
+                    counter += 1
                     text = text.strip()
                     if DEBUG:
                         print('{1}: received text "{0}" at {2}'
                               .format(text, counter, receive_time))
+                    if counter == 0 and not text:
+                        # if reader runs stat() before we write, we might get
+                        # a warning and one empty read here
+                        counter -= 1
+                        warn('Got an empty read, you should have seen another '
+                             'warning about file shrinking',
+                             category=LogReadWarning)
+                        continue
                     index = text.index(':')
                     count_text = int(text[:index].strip())
                     self.assertEqual(count_text, counter)