unittest: Log failure tracebacks at test end.

Store traceback details for each test failure and log to console at the
end of the test, like CPython version of the module does.

python-stdlib/unittest/unittest.py

@@ -1,5 +1,13 @@
 import sys
 
+try:
+    import io
+    import traceback
+except ImportError:
+    import uio as io
+
+    traceback = None
+
 
 class SkipTest(Exception):
     pass
@@ -160,7 +168,7 @@ class TestRunner:
     def run(self, suite):
         res = TestResult()
         for c in suite.tests:
-            run_class(c, res)
+            res.exceptions.extend(run_class(c, res))
 
         print("Ran %d tests\n" % res.testsRun)
         if res.failuresNum > 0 or res.errorsNum > 0:
@@ -180,16 +188,27 @@ class TestResult:
         self.failuresNum = 0
         self.skippedNum = 0
         self.testsRun = 0
+        self.exceptions = []
 
     def wasSuccessful(self):
         return self.errorsNum == 0 and self.failuresNum == 0
 
 
+def capture_exc(e):
+    buf = io.StringIO()
+    if hasattr(sys, "print_exception"):
+        sys.print_exception(e, buf)
+    elif traceback is not None:
+        traceback.print_exception(None, e, sys.exc_info()[2], file=buf)
+    return buf.getvalue()
+
+
 # TODO: Uncompliant
 def run_class(c, test_result):
     o = c()
     set_up = getattr(o, "setUp", lambda: None)
     tear_down = getattr(o, "tearDown", lambda: None)
+    exceptions = []
     for name in dir(o):
         if name.startswith("test"):
             print("%s (%s) ..." % (name, c.__qualname__), end="")
@@ -202,14 +221,14 @@ def run_class(c, test_result):
             except SkipTest as e:
                 print(" skipped:", e.args[0])
                 test_result.skippedNum += 1
-            except:
+            except Exception as ex:
+                exceptions.append(capture_exc(ex))
                 print(" FAIL")
                 test_result.failuresNum += 1
-                # Uncomment to investigate failure in detail
-                # raise
                 continue
             finally:
                 tear_down()
+    return exceptions
 
 
 def main(module="__main__"):
@@ -225,5 +244,9 @@ def main(module="__main__"):
         suite.addTest(c)
     runner = TestRunner()
     result = runner.run(suite)
+    if result.exceptions:
+        sep = "\n----------------------------------------------------------------------\n"
+        print(sep)
+        print(sep.join(result.exceptions))
     # Terminate with non zero return code in case of failures
     sys.exit(result.failuresNum > 0)