Fix MockFileSystem.walk and add test.

third_party/WebKit/Tools/Scripts/webkitpy/common/system/filesystem_mock_walk_unittest.py

Index: third_party/WebKit/Tools/Scripts/webkitpy/common/system/filesystem_mock_walk_unittest.py
diff --git a/third_party/WebKit/Tools/Scripts/webkitpy/common/system/filesystem_mock_unittest.py b/third_party/WebKit/Tools/Scripts/webkitpy/common/system/filesystem_mock_walk_unittest.py
similarity index 88%
copy from third_party/WebKit/Tools/Scripts/webkitpy/common/system/filesystem_mock_unittest.py
copy to third_party/WebKit/Tools/Scripts/webkitpy/common/system/filesystem_mock_walk_unittest.py
index 561959ad5610989b637af3d5c0ee344c251afb2b..c0abdc462041f847709e988f99cd6d65f8fcdb7d 100644
--- a/third_party/WebKit/Tools/Scripts/webkitpy/common/system/filesystem_mock_unittest.py
+++ b/third_party/WebKit/Tools/Scripts/webkitpy/common/system/filesystem_mock_walk_unittest.py
@@ -28,10 +28,17 @@
 
 import unittest
 
-
+from webkitpy.common.host_mock import MockHost
 from webkitpy.common.system import filesystem_mock
+from webkitpy.common.system.filesystem_mock import MockFileSystem
 from webkitpy.common.system import filesystem_unittest
 
+MOCK_DIR = 'foo'
+MOCK_FILES = {'foo/bar/baz': '',
+              'foo/a': '',
+              'foo/b': '',
+              'foo/c': ''}

[qyearsley, 2016/06/01 23:08:43]

These don't have to be globals now; they could be moved into the one test method
that uses them. (And they don't have to be assigned variable names; they can be
passed as literals to the functions that take them.)

Other test methods will likely want to use different file mappings.

Good test methods generally:

 - are simple and flat
 - contain literal values that are easy to understand
 - can be understood by just looking at that one test method

+
 
 class MockFileSystemTest(unittest.TestCase, filesystem_unittest.GenericFileSystemTests):
 
@@ -84,3 +91,9 @@ class MockFileSystemTest(unittest.TestCase, filesystem_unittest.GenericFileSyste
 
     def test_relpath_win32(self):
         pass
+
+    def test_filesystem_walk(self):

[qyearsley, 2016/06/01 23:08:43]

I'm not quite sure whether this walk method will work with directories that are
more deeply nested, e.g.:

foo
├── bar
│   └── baz
│        └── quux
├── a
│   └── x
│       └── y
│           └── z
├── b
└── c

I think it would be helpful to add a separate test method that tests a more
deeply nested directory structure, to check that this "walk" is walking through
the directories recursively to an arbitrary depth.

+        host = MockHost()
+        host.filesystem = MockFileSystem(files=MOCK_FILES)
+        host.filesystem.walk(MOCK_DIR)

[qyearsley, 2016/06/01 23:08:43]

self.assertEqual(
    [
        ('foo', ['bar'], ['a', 'b', 'c']),
        ('foo/bar', [], ['baz']),
    ]
    host.filesystem.walk(MOCK_DIR))

+        self.assertTrue(False)

[qyearsley, 2016/06/01 23:08:43]

This line should be removed.