tests: fix dirty page logging test

Assert that the first time the dirty page metric is logged, the value is
0, but the next time (triggered with the FlushMetrics command) it is a
positive number.

Fixes #845

Signed-off-by: Alexandra Iordache <[email protected]>

Author: Alexandra Iordache

tests/integration_tests/functional/test_logging.py

@@ -8,7 +8,7 @@
 import json
 import os
 import re
-from time import strptime
+from time import sleep, strptime
 
 import host_tools.logging as log_tools
 
@@ -140,11 +140,13 @@ def test_dirty_page_metrics(test_microvm_with_api):
 
     microvm.start()
 
-    lines = metrics_fifo.sequential_reader(3)
-    for line in lines:
-        assert int(json.loads(line)['memory']['dirty_pages']) >= 0
-        # TODO force metrics flushing and get real data without waiting for
-        # Firecracker to flush periodically.
+    sleep(0.3)
+    response = microvm.actions.put(action_type='FlushMetrics')
+    assert microvm.api_session.is_good_response(response.status_code)
+
+    lines = metrics_fifo.sequential_reader(2)
+    assert int(json.loads(lines[0])['memory']['dirty_pages']) == 0
+    assert int(json.loads(lines[1])['memory']['dirty_pages']) > 0
 
 
 def log_file_contains_strings(log_fifo, string_list):