Improve the description for several filesystem matchers.

testtools/matchers/_filesystem.py

@@ -22,6 +22,7 @@
     )
 from ._impl import (
     Matcher,
+    OverrideDescription,
     )
 
 
@@ -32,23 +33,29 @@ def PathExists():
 
       assertThat('/some/path', PathExists())
     """
-    return MatchesPredicate(os.path.exists, "%s does not exist.")
+    return OverrideDescription(
+        'PathExists()',
+        MatchesPredicate(os.path.exists, "%s does not exist."))
 
 
 def DirExists():
     """Matches if the path exists and is a directory."""
-    return MatchesAll(
-        PathExists(),
-        MatchesPredicate(os.path.isdir, "%s is not a directory."),
-        first_only=True)
+    return OverrideDescription(
+        'DirExists()',
+        MatchesAll(
+            PathExists(),
+            MatchesPredicate(os.path.isdir, "%s is not a directory."),
+            first_only=True))
 
 
 def FileExists():
     """Matches if the given path exists and is a file."""
-    return MatchesAll(
-        PathExists(),
-        MatchesPredicate(os.path.isfile, "%s is not a file."),
-        first_only=True)
+    return OverrideDescription(
+        "FileExists()",
+        MatchesAll(
+            PathExists(),
+            MatchesPredicate(os.path.isfile, "%s is not a file."),
+            first_only=True))
 
 
 class DirContains(Matcher):

testtools/matchers/_impl.py

@@ -168,6 +168,19 @@ def get_details(self):
         return self.original.get_details()
 
 
+class OverrideDescription(object):
+
+    def __init__(self, description, wrapped):
+        self._description = description
+        self._wrapped = wrapped
+
+    def __getattr__(self, attr):
+        return getattr(self._wrapped, attr)
+
+    def __str__(self):
+        return self._description
+
+
 # Signal that this is part of the testing framework, and that code from this
 # should not normally appear in tracebacks.
 __unittest = True

testtools/tests/matchers/test_filesystem.py

@@ -53,6 +53,9 @@ def test_not_exists(self):
         self.assertThat(
             "%s does not exist." % doesntexist, Equals(mismatch.describe()))
 
+    def test__str__(self):
+        self.assertEqual("PathExists()", str(PathExists()))
+
 
 class TestDirExists(TestCase, PathHelpers):
 
@@ -74,6 +77,9 @@ def test_not_a_directory(self):
         self.assertThat(
             "%s is not a directory." % filename, Equals(mismatch.describe()))
 
+    def test__str__(self):
+        self.assertEqual("DirExists()", str(DirExists()))
+
 
 class TestFileExists(TestCase, PathHelpers):
 
@@ -96,6 +102,9 @@ def test_not_a_file(self):
         self.assertThat(
             "%s is not a file." % tempdir, Equals(mismatch.describe()))
 
+    def test__str__(self):
+        self.assertEqual("FileExists()", str(FileExists()))
+
 
 class TestDirContains(TestCase, PathHelpers):