[3.10] bpo-13236: Flush the output stream more often in unittest (GH-29929) (GH-30039)

It can prevent some losses when output to buffered stream..
(cherry picked from commit 83fa1291fd)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>

Lib/unittest/runner.py

@@ -59,6 +59,7 @@ class TextTestResult(result.TestResult):
         super(TextTestResult, self).addSuccess(test)
         if self.showAll:
             self.stream.writeln("ok")
+            self.stream.flush()
         elif self.dots:
             self.stream.write('.')
             self.stream.flush()
@@ -67,6 +68,7 @@ class TextTestResult(result.TestResult):
         super(TextTestResult, self).addError(test, err)
         if self.showAll:
             self.stream.writeln("ERROR")
+            self.stream.flush()
         elif self.dots:
             self.stream.write('E')
             self.stream.flush()
@@ -75,6 +77,7 @@ class TextTestResult(result.TestResult):
         super(TextTestResult, self).addFailure(test, err)
         if self.showAll:
             self.stream.writeln("FAIL")
+            self.stream.flush()
         elif self.dots:
             self.stream.write('F')
             self.stream.flush()
@@ -83,6 +86,7 @@ class TextTestResult(result.TestResult):
         super(TextTestResult, self).addSkip(test, reason)
         if self.showAll:
             self.stream.writeln("skipped {0!r}".format(reason))
+            self.stream.flush()
         elif self.dots:
             self.stream.write("s")
             self.stream.flush()
@@ -91,6 +95,7 @@ class TextTestResult(result.TestResult):
         super(TextTestResult, self).addExpectedFailure(test, err)
         if self.showAll:
             self.stream.writeln("expected failure")
+            self.stream.flush()
         elif self.dots:
             self.stream.write("x")
             self.stream.flush()
@@ -99,6 +104,7 @@ class TextTestResult(result.TestResult):
         super(TextTestResult, self).addUnexpectedSuccess(test)
         if self.showAll:
             self.stream.writeln("unexpected success")
+            self.stream.flush()
         elif self.dots:
             self.stream.write("u")
             self.stream.flush()
@@ -106,6 +112,7 @@ class TextTestResult(result.TestResult):
     def printErrors(self):
         if self.dots or self.showAll:
             self.stream.writeln()
+            self.stream.flush()
         self.printErrorList('ERROR', self.errors)
         self.printErrorList('FAIL', self.failures)
 
@@ -115,6 +122,7 @@ class TextTestResult(result.TestResult):
             self.stream.writeln("%s: %s" % (flavour,self.getDescription(test)))
             self.stream.writeln(self.separator2)
             self.stream.writeln("%s" % err)
+            self.stream.flush()
 
 
 class TextTestRunner(object):
@@ -218,4 +226,5 @@ class TextTestRunner(object):
             self.stream.writeln(" (%s)" % (", ".join(infos),))
         else:
             self.stream.write("\n")
+        self.stream.flush()
         return result

Lib/unittest/test/test_program.py

@@ -6,6 +6,7 @@ import subprocess
 from test import support
 import unittest
 import unittest.test
+from .test_result import BufferedWriter
 
 
 class Test_TestProgram(unittest.TestCase):
@@ -104,30 +105,39 @@ class Test_TestProgram(unittest.TestCase):
                           program.testNames)
 
     def test_NonExit(self):
+        stream = BufferedWriter()
         program = unittest.main(exit=False,
                                 argv=["foobar"],
-                                testRunner=unittest.TextTestRunner(stream=io.StringIO()),
+                                testRunner=unittest.TextTestRunner(stream=stream),
                                 testLoader=self.FooBarLoader())
         self.assertTrue(hasattr(program, 'result'))
+        self.assertIn('\nFAIL: testFail ', stream.getvalue())
+        self.assertTrue(stream.getvalue().endswith('\n\nFAILED (failures=1)\n'))
 
 
     def test_Exit(self):
+        stream = BufferedWriter()
         self.assertRaises(
             SystemExit,
             unittest.main,
             argv=["foobar"],
-            testRunner=unittest.TextTestRunner(stream=io.StringIO()),
+            testRunner=unittest.TextTestRunner(stream=stream),
             exit=True,
             testLoader=self.FooBarLoader())
+        self.assertIn('\nFAIL: testFail ', stream.getvalue())
+        self.assertTrue(stream.getvalue().endswith('\n\nFAILED (failures=1)\n'))
 
 
     def test_ExitAsDefault(self):
+        stream = BufferedWriter()
         self.assertRaises(
             SystemExit,
             unittest.main,
             argv=["foobar"],
-            testRunner=unittest.TextTestRunner(stream=io.StringIO()),
+            testRunner=unittest.TextTestRunner(stream=stream),
             testLoader=self.FooBarLoader())
+        self.assertIn('\nFAIL: testFail ', stream.getvalue())
+        self.assertTrue(stream.getvalue().endswith('\n\nFAILED (failures=1)\n'))
 
 
 class InitialisableProgram(unittest.TestProgram):

Lib/unittest/test/test_result.py

@@ -34,6 +34,22 @@ def bad_cleanup2():
     raise ValueError('bad cleanup2')
 
 
+class BufferedWriter:
+    def __init__(self):
+        self.result = ''
+        self.buffer = ''
+
+    def write(self, arg):
+        self.buffer += arg
+
+    def flush(self):
+        self.result += self.buffer
+        self.buffer = ''
+
+    def getvalue(self):
+        return self.result
+
+
 class Test_TestResult(unittest.TestCase):
     # Note: there are not separate tests for TestResult.wasSuccessful(),
     # TestResult.errors, TestResult.failures, TestResult.testsRun or
@@ -445,10 +461,13 @@ class Test_TestResult(unittest.TestCase):
         self.assertTrue(result.shouldStop)
 
     def testFailFastSetByRunner(self):
-        runner = unittest.TextTestRunner(stream=io.StringIO(), failfast=True)
+        stream = BufferedWriter()
+        runner = unittest.TextTestRunner(stream=stream, failfast=True)
         def test(result):
             self.assertTrue(result.failfast)
         result = runner.run(test)
+        stream.flush()
+        self.assertTrue(stream.getvalue().endswith('\n\nOK\n'))
 
 
 classDict = dict(unittest.TestResult.__dict__)

Misc/NEWS.d/next/Library/2021-11-30-13-52-02.bpo-13236.FmJIkO.rst

@@ -0,0 +1,2 @@
+:class:`unittest.TextTestResult` and :class:`unittest.TextTestRunner` flush
+now the output stream more often.