unit test on buildbot.steps.transfer._FileWriter.__init__()

Test creating an instance of _FileWrite class. Test the code path
where destfile's parent directory is created.

master/buildbot/test/unit/test_steps_transfer.py

@@ -18,6 +18,7 @@
 import tempfile, os
 import shutil
 import tarfile
+import stat
 from twisted.trial import unittest
 
 from mock import Mock
@@ -33,6 +34,46 @@
 from buildbot.test.fake.remotecommand import Expect, ExpectRemoteRef
 
 
+# Test buildbot.steps.transfer._FileWriter class.
+class TestFileWriter(unittest.TestCase):
+
+    # test _FileWrite.__init__() method.
+    def testInit(self):
+        #
+        # patch functions called in constructor
+        #
+
+        # patch os.path.exists() to always return False
+        mockedExists = Mock(return_value=False)
+        self.patch(os.path, "exists", mockedExists)
+
+        # capture calls to os.makedirs()
+        mockedMakedirs = Mock()
+        self.patch(os, 'makedirs', mockedMakedirs)
+
+        # capture calls to tempfile.mkstemp()
+        mockedMkstemp = Mock(return_value=(7, "tmpname"))
+        self.patch(tempfile, "mkstemp", mockedMkstemp)
+
+        # capture calls to os.fdopen()
+        mockedFdopen = Mock()
+        self.patch(os, "fdopen", mockedFdopen)
+
+        #
+        # call _FileWriter constructor
+        #
+        destfile = os.path.join("dir", "file")
+        transfer._FileWriter(destfile, 64, stat.S_IRUSR)
+
+        #
+        # validate captured calls
+        #
+        absdir = os.path.dirname(os.path.abspath(os.path.join("dir", "file")))
+        mockedExists.assert_called_once_with(absdir)
+        mockedMakedirs.assert_called_once_with(absdir)
+        mockedMkstemp.assert_called_once_with(dir=absdir)
+        mockedFdopen.assert_called_once_with(7, 'wb')
+
 # Test buildbot.steps.transfer._TransferBuildStep class.
 class TestTransferBuildStep(unittest.TestCase):