tests: make subprocess handling reusable for different tests in test-stdio.py

tests/test-stdio.py

@@ -1,133 +1,150 b''
 #!/usr/bin/env python
 """
 Tests the buffering behavior of stdio streams in `mercurial.utils.procutil`.
 """
 from __future__ import absolute_import
 
 import contextlib
 import errno
 import os
 import subprocess
 import sys
 import unittest
 
 from mercurial import pycompat
 
 
-BUFFERING_CHILD_SCRIPT = r'''
+TEST_BUFFERING_CHILD_SCRIPT = r'''
 import os
 
 from mercurial import dispatch
 from mercurial.utils import procutil
 
 dispatch.initstdio()
 procutil.{stream}.write(b'aaa')
 os.write(procutil.{stream}.fileno(), b'[written aaa]')
 procutil.{stream}.write(b'bbb\n')
 os.write(procutil.{stream}.fileno(), b'[written bbb\\n]')
 '''
 UNBUFFERED = b'aaa[written aaa]bbb\n[written bbb\\n]'
 LINE_BUFFERED = b'[written aaa]aaabbb\n[written bbb\\n]'
 FULLY_BUFFERED = b'[written aaa][written bbb\\n]aaabbb\n'
 
 
 @contextlib.contextmanager
 def _closing(fds):
     try:
         yield
     finally:
         for fd in fds:
             try:
                 os.close(fd)
             except EnvironmentError:
                 pass
 
 
 @contextlib.contextmanager
 def _pipes():
     rwpair = os.pipe()
     with _closing(rwpair):
         yield rwpair
 
 
 @contextlib.contextmanager
 def _ptys():
     if pycompat.iswindows:
         raise unittest.SkipTest("PTYs are not supported on Windows")
     import pty
     import tty
 
     rwpair = pty.openpty()
     with _closing(rwpair):
         tty.setraw(rwpair[0])
         yield rwpair
 
 
 def _readall(fd, buffer_size):
     buf = []
     while True:
         try:
             s = os.read(fd, buffer_size)
         except OSError as e:
             if e.errno == errno.EIO:
                 # If the child-facing PTY got closed, reading from the
                 # parent-facing PTY raises EIO.
                 break
             raise
         if not s:
             break
         buf.append(s)
     return b''.join(buf)
 
 
 class TestStdio(unittest.TestCase):
-    def _test(self, stream, rwpair_generator, expected_output, python_args=[]):
+    def _test(
+        self,
+        child_script,
+        stream,
+        rwpair_generator,
+        check_output,
+        python_args=[],
+    ):
         assert stream in ('stdout', 'stderr')
         with rwpair_generator() as (stream_receiver, child_stream), open(
             os.devnull, 'rb'
         ) as child_stdin:
             proc = subprocess.Popen(
-                [sys.executable]
-                + python_args
-                + ['-c', BUFFERING_CHILD_SCRIPT.format(stream=stream)],
+                [sys.executable] + python_args + ['-c', child_script],
                 stdin=child_stdin,
                 stdout=child_stream if stream == 'stdout' else None,
                 stderr=child_stream if stream == 'stderr' else None,
             )
             try:
                 os.close(child_stream)
-                self.assertEqual(
-                    _readall(stream_receiver, 1024), expected_output
-                )
+                check_output(stream_receiver)
             except:  # re-raises
                 proc.terminate()
                 raise
             finally:
                 retcode = proc.wait()
             self.assertEqual(retcode, 0)
 
+    def _test_buffering(
+        self, stream, rwpair_generator, expected_output, python_args=[]
+    ):
+        def check_output(stream_receiver):
+            self.assertEqual(_readall(stream_receiver, 1024), expected_output)
+
+        self._test(
+            TEST_BUFFERING_CHILD_SCRIPT.format(stream=stream),
+            stream,
+            rwpair_generator,
+            check_output,
+            python_args,
+        )
+
     def test_buffering_stdout_pipes(self):
-        self._test('stdout', _pipes, FULLY_BUFFERED)
+        self._test_buffering('stdout', _pipes, FULLY_BUFFERED)
 
     def test_buffering_stdout_ptys(self):
-        self._test('stdout', _ptys, LINE_BUFFERED)
+        self._test_buffering('stdout', _ptys, LINE_BUFFERED)
 
     def test_buffering_stdout_pipes_unbuffered(self):
-        self._test('stdout', _pipes, UNBUFFERED, python_args=['-u'])
+        self._test_buffering('stdout', _pipes, UNBUFFERED, python_args=['-u'])
 
     def test_buffering_stdout_ptys_unbuffered(self):
-        self._test('stdout', _ptys, UNBUFFERED, python_args=['-u'])
+        self._test_buffering('stdout', _ptys, UNBUFFERED, python_args=['-u'])
 
     if not pycompat.ispy3 and not pycompat.iswindows:
         # On Python 2 on non-Windows, we manually open stdout in line-buffered
         # mode if connected to a TTY. We should check if Python was configured
         # to use unbuffered stdout, but it's hard to do that.
         test_buffering_stdout_ptys_unbuffered = unittest.expectedFailure(
             test_buffering_stdout_ptys_unbuffered
         )
 
 
 if __name__ == '__main__':
     import silenttestrunner
 
     silenttestrunner.main(__name__)