capture: track current state in _state attributes

This is meant for debugging, and making assertions later.

src/_pytest/capture.py

@@ -456,6 +456,7 @@ CaptureResult = collections.namedtuple("CaptureResult", ["out", "err"])
 
 class MultiCapture(object):
     out = err = in_ = None
+    _state = None
 
     def __init__(self, out=True, err=True, in_=True, Capture=None):
         if in_:
@@ -466,9 +467,16 @@ class MultiCapture(object):
             self.err = Capture(2)
 
     def __repr__(self):
-        return "<MultiCapture out=%r err=%r in_=%r>" % (self.out, self.err, self.in_)
+        return "<MultiCapture out=%r err=%r in_=%r _state=%r _in_suspended=%r>" % (
+            self.out,
+            self.err,
+            self.in_,
+            self._state,
+            getattr(self, "_in_suspended", "<UNSET>"),
+        )
 
     def start_capturing(self):
+        self._state = "started"
         if self.in_:
             self.in_.start()
         if self.out:
@@ -486,6 +494,7 @@ class MultiCapture(object):
         return out, err
 
     def suspend_capturing(self, in_=False):
+        self._state = "suspended"
         if self.out:
             self.out.suspend()
         if self.err:
@@ -495,6 +504,7 @@ class MultiCapture(object):
             self._in_suspended = True
 
     def resume_capturing(self):
+        self._state = "resumed"
         if self.out:
             self.out.resume()
         if self.err:
@@ -505,9 +515,9 @@ class MultiCapture(object):
 
     def stop_capturing(self):
         """ stop capturing and reset capturing streams """
-        if hasattr(self, "_reset"):
+        if self._state == "stopped":
             raise ValueError("was already stopped")
-        self._reset = True
+        self._state = "stopped"
         if self.out:
             self.out.done()
         if self.err:
@@ -535,6 +545,7 @@ class FDCaptureBinary(object):
     """
 
     EMPTY_BUFFER = b""
+    _state = None
 
     def __init__(self, targetfd, tmpfile=None):
         self.targetfd = targetfd
@@ -561,9 +572,10 @@ class FDCaptureBinary(object):
             self.tmpfile_fd = tmpfile.fileno()
 
     def __repr__(self):
-        return "<FDCapture %s oldfd=%s>" % (
+        return "<FDCapture %s oldfd=%s _state=%r>" % (
             self.targetfd,
             getattr(self, "targetfd_save", None),
+            self._state,
         )
 
     def start(self):
@@ -574,6 +586,7 @@ class FDCaptureBinary(object):
             raise ValueError("saved filedescriptor not valid anymore")
         os.dup2(self.tmpfile_fd, self.targetfd)
         self.syscapture.start()
+        self._state = "started"
 
     def snap(self):
         self.tmpfile.seek(0)
@@ -590,14 +603,17 @@ class FDCaptureBinary(object):
         os.close(targetfd_save)
         self.syscapture.done()
         _attempt_to_close_capture_file(self.tmpfile)
+        self._state = "done"
 
     def suspend(self):
         self.syscapture.suspend()
         os.dup2(self.targetfd_save, self.targetfd)
+        self._state = "suspended"
 
     def resume(self):
         self.syscapture.resume()
         os.dup2(self.tmpfile_fd, self.targetfd)
+        self._state = "resumed"
 
     def writeorg(self, data):
         """ write to original file descriptor. """
@@ -625,6 +641,7 @@ class FDCapture(FDCaptureBinary):
 class SysCapture(object):
 
     EMPTY_BUFFER = str()
+    _state = None
 
     def __init__(self, fd, tmpfile=None):
         name = patchsysdict[fd]
@@ -637,8 +654,17 @@ class SysCapture(object):
                 tmpfile = CaptureIO()
         self.tmpfile = tmpfile
 
+    def __repr__(self):
+        return "<SysCapture %s _old=%r, tmpfile=%r _state=%r>" % (
+            self.name,
+            self._old,
+            self.tmpfile,
+            self._state,
+        )
+
     def start(self):
         setattr(sys, self.name, self.tmpfile)
+        self._state = "started"
 
     def snap(self):
         res = self.tmpfile.getvalue()
@@ -650,12 +676,15 @@ class SysCapture(object):
         setattr(sys, self.name, self._old)
         del self._old
         _attempt_to_close_capture_file(self.tmpfile)
+        self._state = "done"
 
     def suspend(self):
         setattr(sys, self.name, self._old)
+        self._state = "suspended"
 
     def resume(self):
         setattr(sys, self.name, self.tmpfile)
+        self._state = "resumed"
 
     def writeorg(self, data):
         self._old.write(data)

testing/test_capture.py

@@ -1243,25 +1243,24 @@ class TestStdCaptureFDinvalidFD(object):
             from _pytest import capture
 
             def StdCaptureFD(out=True, err=True, in_=True):
-                return capture.MultiCapture(out, err, in_,
-                                            Capture=capture.FDCapture)
+                return capture.MultiCapture(out, err, in_, Capture=capture.FDCapture)
 
             def test_stdout():
                 os.close(1)
                 cap = StdCaptureFD(out=True, err=False, in_=False)
-                assert repr(cap.out) == "<FDCapture 1 oldfd=None>"
+                assert repr(cap.out) == "<FDCapture 1 oldfd=None _state=None>"
                 cap.stop_capturing()
 
             def test_stderr():
                 os.close(2)
                 cap = StdCaptureFD(out=False, err=True, in_=False)
-                assert repr(cap.err) == "<FDCapture 2 oldfd=None>"
+                assert repr(cap.err) == "<FDCapture 2 oldfd=None _state=None>"
                 cap.stop_capturing()
 
             def test_stdin():
                 os.close(0)
                 cap = StdCaptureFD(out=False, err=False, in_=True)
-                assert repr(cap.in_) == "<FDCapture 0 oldfd=None>"
+                assert repr(cap.in_) == "<FDCapture 0 oldfd=None _state=None>"
                 cap.stop_capturing()
         """
         )