avocado/utils/process.py: make CmdResult.std{out,err}_text smarter

In situations where a user of the CmdResult class manually sets the
stdout/stderr attributes to a string, instead of the recommended and
documented content of type "bytes", it won't be possible to "decode"
the bytes into a string of a given encoding, and we'll end up with
a crash.

Since the goal of std{out,err}_text is to return a text version
of stdout, if itself already is of such a type, let's just return
it.

Additionally, if the data cannot be "decode()d", let's raise an
explicit TypeError on this location, rather than later in the code
when its value is attempted to be used.
Signed-off-by: NCleber Rosa <crosa@redhat.com>

avocado/utils/process.py

@@ -32,6 +32,7 @@ import threading
 import time
 
 from io import BytesIO
+from six import string_types
 
 from . import gdb
 from . import runtime
@@ -294,11 +295,19 @@ class CmdResult(object):
 
     @property
     def stdout_text(self):
+        if type(self.stdout) in string_types:
+            return self.stdout
+        if hasattr(self.stdout, 'decode'):
             return self.stdout.decode(self.encoding)
+        raise TypeError("Unable to decode stdout into a string-like type")
 
     @property
     def stderr_text(self):
+        if type(self.stderr) in string_types:
+            return self.stderr
+        if hasattr(self.stderr, 'decode'):
             return self.stderr.decode(self.encoding)
+        raise TypeError("Unable to decode stderr into a string-like type")
 
     def __repr__(self):
         cmd_rep = ("Command: %s\n"

selftests/unit/test_utils_process.py

@@ -12,6 +12,9 @@ from avocado.utils import gdb
 from avocado.utils import process
 from avocado.utils import path
 
+from six import string_types
+
+
 TRUE_CMD = path.find_command('true')
 
 
@@ -231,6 +234,33 @@ class MiscProcessTests(unittest.TestCase):
         self.assertEqual("./bin", res)
 
 
+class CmdResultTests(unittest.TestCase):
+
+    def test_cmd_result_stdout_stderr_bytes(self):
+        result = process.CmdResult()
+        self.assertTrue(isinstance(result.stdout, bytes))
+        self.assertTrue(isinstance(result.stderr, bytes))
+
+    def test_cmd_result_stdout_stderr_text(self):
+        result = process.CmdResult()
+        self.assertTrue(isinstance(result.stdout_text, string_types))
+        self.assertTrue(isinstance(result.stderr_text, string_types))
+
+    def test_cmd_result_stdout_stderr_already_text(self):
+        result = process.CmdResult()
+        result.stdout = "supposed command output, but not as bytes"
+        result.stderr = "supposed command error, but not as bytes"
+        self.assertEqual(result.stdout, result.stdout_text)
+        self.assertEqual(result.stderr, result.stderr_text)
+
+    def test_cmd_result_stdout_stderr_other_type(self):
+        result = process.CmdResult()
+        result.stdout = None
+        result.stderr = None
+        self.assertRaises(TypeError, lambda x: result.stdout_text)
+        self.assertRaises(TypeError, lambda x: result.stderr_text)
+
+
 class FDDrainerTests(unittest.TestCase):
 
     def test_drain_from_pipe_fd(self):