Merge pull request Pyomo#3560 from jsiirola/tee-test-fixes

Address two intermittent test failures when capturing output

Author: jsiirola

Diff for: pyomo/common/tee.py

@@ -120,9 +120,11 @@ def __init__(self, fd=1, output=None, synchronize=True):
 
     def __enter__(self):
         if self.std:
+            # We used to flush original_file here.  We have removed that
+            # because the std* streams are flushed by capture_output.
+            # Flushing again here caused intermittent errors due to
+            # closed file handles on OSX
             self.original_file = getattr(sys, self.std)
-            # important: flush the current file buffer when redirecting
-            self.original_file.flush()
         # Duplicate the original standard file descriptor(file
         # descriptor 1 or 2) to a different file descriptor number
         self.original_fd = os.dup(self.fd)

Diff for: pyomo/common/tests/test_tee.py

@@ -589,8 +589,18 @@ def test_exit_on_del(self):
         remaining_attempts = 4
         while len(stack) and remaining_attempts:
             gc.collect()
+            time.sleep(((4 - remaining_attempts) / 4.0) ** 2)
             remaining_attempts -= 1
-        self.assertEqual(len(stack), 0)
+        try:
+            self.assertEqual(len(stack), 0)
+        except:
+            # We still want to unwind the context managers if the test fails:
+            while stack:
+                try:
+                    stack.pop().__exit__(None, None, None)
+                except:
+                    pass
+            raise
 
     def test_deadlock(self):
         class MockStream(object):