unittests: mock out rustfmt

We don't need to have rustfmt installed here.

BUG=None
TEST=`./pre-upload_unittest.py` passes

Change-Id: I00acb8d7e2fcde43e4e0d746d10335f876ed46b9
Reviewed-on: https://chromium-review.googlesource.com/1762358
Tested-by: Mike Frysinger <vapier@chromium.org>
Commit-Ready: Mike Frysinger <vapier@chromium.org>
Legacy-Commit-Queue: Commit Bot <commit-bot@chromium.org>
Reviewed-by: Fletcher Woodruff <fletcherw@chromium.org>
diff --git a/pre-upload_unittest.py b/pre-upload_unittest.py
index 640aef8..88d665b 100755
--- a/pre-upload_unittest.py
+++ b/pre-upload_unittest.py
@@ -1632,7 +1632,9 @@
   def testBadRustFile(self):
     self.PatchObject(pre_upload, '_get_affected_files', return_value=['a.rs'])
     # Bad because it's missing trailing newline.
-    self.content_mock.return_value = 'fn main() {}'
+    content = 'fn main() {}'
+    self.content_mock.return_value = content
+    self.PatchObject(pre_upload, '_run_command', return_value=content + '\n')
     failure = pre_upload._check_rustfmt(ProjectNamed('PROJECT'), 'COMMIT')
     self.assertIsNotNone(failure)
     self.assertEquals('Files not formatted with rustfmt: '
@@ -1642,7 +1644,9 @@
 
   def testGoodRustFile(self):
     self.PatchObject(pre_upload, '_get_affected_files', return_value=['a.rs'])
-    self.content_mock.return_value = 'fn main() {}\n'
+    content = 'fn main() {}\n'
+    self.content_mock.return_value = content
+    self.PatchObject(pre_upload, '_run_command', return_value=content)
     failure = pre_upload._check_rustfmt(ProjectNamed('PROJECT'), 'COMMIT')
     self.assertIsNone(failure)