[PATCH v2 1/5] qemu-iotests: do not buffer the test output

[Paolo Bonzini <pbonzini@redhat.com>]

Instead of buffering the test output into a StringIO, patch it on
the fly by wrapping sys.stdout's write method.  This can be
done unconditionally, even if using -d, which makes execute_unittest
a bit simpler.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
---
 tests/qemu-iotests/iotests.py | 68 ++++++++++++++++++++---------------
 1 file changed, 40 insertions(+), 28 deletions(-)

diff --git a/tests/qemu-iotests/iotests.py b/tests/qemu-iotests/iotests.py
index 90d0b62523..0521235030 100644
--- a/tests/qemu-iotests/iotests.py
+++ b/tests/qemu-iotests/iotests.py
@@ -32,7 +32,7 @@
 import sys
 import time
 from typing import (Any, Callable, Dict, Iterable,
-                    List, Optional, Sequence, Tuple, TypeVar)
+                    List, Optional, Sequence, Tuple, Type, TypeVar)
 import unittest
 
 from contextlib import contextmanager
@@ -1271,37 +1271,49 @@ def func_wrapper(*args, **kwargs):
             return func(*args, **kwargs)
     return func_wrapper
 
+# We need to filter out the time taken from the output so that
+# qemu-iotest can reliably diff the results against master output,
+# and hide skipped tests from the reference output.
+
+class ReproducibleTestResult(unittest.TextTestResult):
+    def addSkip(self, test, reason):
+        # Same as TextTestResult, but print dot instead of "s"
+        unittest.TestResult.addSkip(self, test, reason)
+        if self.showAll:
+            self.stream.writeln("skipped {0!r}".format(reason))
+        elif self.dots:
+            self.stream.write(".")
+            self.stream.flush()
+
+class ReproducibleStreamWrapper(object):
+    def __init__(self, stream):
+        self.stream = stream
+
+    def __getattr__(self, attr):
+        if attr in ('stream', '__getstate__'):
+            raise AttributeError(attr)
+        return getattr(self.stream,attr)
+
+    def write(self, arg=None):
+        arg = re.sub(r'Ran (\d+) tests? in [\d.]+s', r'Ran \1 tests', arg)
+        arg = re.sub(r' \(skipped=\d+\)', r'', arg)
+        self.stream.write(arg)
+
+class ReproducibleTestRunner(unittest.TextTestRunner):
+    def __init__(self, stream: Optional[io.TextIOBase] = None,
+                 resultclass: Type = ReproducibleTestResult, *args, **kwargs):
+        rstream = ReproducibleStreamWrapper(stream or sys.stdout)
+        super().__init__(stream=rstream,           # type: ignore
+                         descriptions=True,
+                         resultclass=resultclass,
+                         *args, **kwargs)
+
 def execute_unittest(debug=False):
     """Executes unittests within the calling module."""
 
     verbosity = 2 if debug else 1
-
-    if debug:
-        output = sys.stdout
-    else:
-        # We need to filter out the time taken from the output so that
-        # qemu-iotest can reliably diff the results against master output.
-        output = io.StringIO()
-
-    runner = unittest.TextTestRunner(stream=output, descriptions=True,
-                                     verbosity=verbosity)
-    try:
-        # unittest.main() will use sys.exit(); so expect a SystemExit
-        # exception
-        unittest.main(testRunner=runner)
-    finally:
-        # We need to filter out the time taken from the output so that
-        # qemu-iotest can reliably diff the results against master output.
-        if not debug:
-            out = output.getvalue()
-            out = re.sub(r'Ran (\d+) tests? in [\d.]+s', r'Ran \1 tests', out)
-
-            # Hide skipped tests from the reference output
-            out = re.sub(r'OK \(skipped=\d+\)', 'OK', out)
-            out_first_line, out_rest = out.split('\n', 1)
-            out = out_first_line.replace('s', '.') + '\n' + out_rest
-
-            sys.stderr.write(out)
+    runner = unittest.ReproducibleTestRunner(verbosity=verbosity)
+    unittest.main(testRunner=runner)
 
 def execute_setup_common(supported_fmts: Sequence[str] = (),
                          supported_platforms: Sequence[str] = (),
-- 
2.30.1