oeqa/selftest: add test case for oeqa.utils.subprocesstweak

This class has a monkey-patched CalledProcessError instance that extends
the __str__ method. Add a test case to ensure that it behaves as
expected.

Signed-off-by: Ross Burton <ross.burton@arm.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

Author: rossburton

meta/lib/oeqa/selftest/cases/liboe.py

@@ -9,7 +9,7 @@
 import oe.path
 import os
 
-class LibOE(OESelftestTestCase):
+class CopyTreeTests(OESelftestTestCase):
 
     @classmethod
     def setUpClass(cls):
@@ -102,3 +102,36 @@ def touchfile(tf):
         self.assertEqual(dstcnt, len(testfiles), "Number of files in dst (%s) differs from number of files in src(%s)." % (dstcnt, srccnt))
 
         oe.path.remove(testloc)
+
+class SubprocessTests(OESelftestTestCase):
+
+    def test_subprocess_tweak(self):
+        """
+        Test that the string representation of
+        oeqa.utils.subprocesstweak.OETestCalledProcessError includes stdout and
+        stderr, as expected.
+        """
+        script = """
+#! /bin/sh
+echo Ivn fgqbhg | tr '[a-zA-Z]' '[n-za-mN-ZA-M]'
+echo Ivn fgqree | tr '[a-zA-Z]' '[n-za-mN-ZA-M]' >&2
+exit 42
+        """
+
+        import subprocess
+        import unittest.mock
+        from oeqa.utils.subprocesstweak import OETestCalledProcessError
+
+        with self.assertRaises(OETestCalledProcessError) as cm:
+            with unittest.mock.patch("subprocess.CalledProcessError", OETestCalledProcessError):
+                subprocess.run(["bash", "-"], input=script, text=True, capture_output=True, check=True)
+
+        e = cm.exception
+        self.assertEqual(e.returncode, 42)
+        self.assertEqual("Via stdout\n", e.stdout)
+        self.assertEqual("Via stderr\n", e.stderr)
+
+        string = str(e)
+        self.assertIn("exit status 42", string)
+        self.assertIn("Standard Output: Via stdout", string)
+        self.assertIn("Standard Error: Via stderr", string)