A hang core = app test does not show an output

[Totktonada]

We can simulate hang 'core = app' test like so:

diff --git a/test/app-tap/tap.test.lua b/test/app-tap/tap.test.lua
index 0e1de7f1c..26db04448 100755
--- a/test/app-tap/tap.test.lua
+++ b/test/app-tap/tap.test.lua
@@ -136,6 +136,16 @@ test:test('like', function(t)
     t:unlike('abcde', 'acd', 'unlike(abcde, acd)')
 end)
 
+if (os.getenv('FLOOD') or ''):len() > 0 then
+    for i = 1, 10000 do
+        print(string.rep('x', 1024))
+    end
+end
+
+while true do
+    require('fiber').sleep(1)
+end
+
 --
 -- Finish root test. Since we used non-callback variant, we have to
 -- call check explicitly.

When 'FLOOD' is set it produces much output to debug w/o paying attention to bufferization.

I tried it with the patch #110 applied. And the following patch applied at top of it:

diff --git a/lib/app_server.py b/lib/app_server.py
index 1346866..de8de04 100644
--- a/lib/app_server.py
+++ b/lib/app_server.py
@@ -16,11 +16,8 @@ from test import TestRunGreenlet, TestExecutionError
 
 
 def run_server(execs, cwd, server, logfile, retval):
-    server.process = Popen(execs, stdout=PIPE, stderr=PIPE, cwd=cwd)
-    stdout, stderr = server.process.communicate()
-    sys.stdout.write(stdout)
     with open(logfile, 'a') as f:
-        f.write(stderr)
+        server.process = Popen(execs, stdout=sys.stdout, stderr=f, cwd=cwd)
     retval['returncode'] = server.process.wait()
     server.process = None
 
diff --git a/lib/test.py b/lib/test.py
index 03360de..2d7aa31 100644
--- a/lib/test.py
+++ b/lib/test.py
@@ -88,6 +88,9 @@ class FilteredStream:
     def flush(self):
         self.stream.flush()
 
+    def fileno(self):
+        return self.stream.fileno()
+
 
 def get_filename_by_test(postfix, test_name):
     rg = re.compile('\.test.*')

TEST_RUN_TESTS=app-tap/tap.test.lua make test does not show any output. But FLOOD=1 TEST_RUN_TESTS=app-tap/tap.test.lua make test does. So we have at least two problems:

• Popen.communicate() does not give us output until a process exits (but please, note, the patch below brokes filters in FilteredStream).
• Despite per-line bufferization set in FilteredStream.__init__() a test inherits a stdout file descriptior that bufferizes output (or smth like so).