unify outcome exceptions

_pytest/outcomes.py

@@ -8,7 +8,10 @@
 import attr
 
 
-@attr.s(frozen=True)
+# str = true ensures repr uses str
+exc = attr.s(frozen=True)
+
+@exc
 class OutcomeException(BaseException):
     """ OutcomeException and its subclass instances indicate and
         contain info about test and collection outcomes.
@@ -31,7 +34,7 @@ def __repr__(self):
 TEST_OUTCOME = (OutcomeException, Exception)
 
 
-@attr.s(frozen=True)
+@exc
 class Skipped(OutcomeException):
     # XXX hackish: on 3k we fake to live in the builtins
     # in order to have Skipped exception printing shorter/nicer
@@ -49,11 +52,13 @@ class Failed(OutcomeException):
     __module__ = 'builtins'
 
 
-@attr.s(frozen=True)
+@exc
 class Exit(KeyboardInterrupt):
     """ raised for immediate program exits (no tracebacks/summaries)"""
     msg = attr.ib(default="unknown reason")
 
+    def __str__(self):
+        return self.msg
 
 # exposed helper methods