rebaseline.py : add self-tests

tools/rebaseline.py

Index: tools/rebaseline.py
===================================================================
--- tools/rebaseline.py	(revision 9425)
+++ tools/rebaseline.py	(working copy)
@@ -17,7 +17,6 @@
 import os
 import subprocess
 import sys
-import tempfile
 
 # Mapping of gm-expectations subdir (under
 # https://skia.googlecode.com/svn/gm-expected/ )
@@ -48,6 +47,9 @@
 }
 
 
+class CommandFailedException(Exception):
+    pass
+
 class Rebaseliner(object):
 
     # params:
@@ -75,30 +77,56 @@
             os.path.exists('.git') or
             os.path.exists(os.path.join(os.pardir, '.git')))
 
-    # Execute subprocess.call(), unless dry_run is True
-    def _Call(self, cmd, stdout=None):
+    # If dry_run is False, execute subprocess.call(cmd).
+    # If dry_run is True, print the command we would have otherwise run.
+    # Raises a CommandFailedException if the command fails.
+    def _Call(self, cmd):
         if self._dry_run:
             print '%s' % ' '.join(cmd)
-            return 0
-        if stdout:
-            return subprocess.call(cmd, stdout=stdout)
-        else:
-            return subprocess.call(cmd)
+            return
+        if subprocess.call(cmd) != 0:
+            raise CommandFailedException('error running command: ' +
+                                         ' '.join(cmd))
 
+    # Download a single file, raising a CommandFailedException if it fails.
+    def _DownloadFile(self, source_url, dest_filename):
+        # Download into a temporary file and then rename it afterwards,
+        # so that we don't corrupt the existing file if it fails midway thru.
+        temp_filename = os.path.join(os.path.dirname(dest_filename),
+                                     '.temp-' + os.path.basename(dest_filename))
+
+        # TODO(epoger): Replace calls to "curl"/"mv" (which will only work on
+        # Unix) with a Python HTTP library (which should work cross-platform)
+        self._Call([ 'curl', '--fail', '--silent', source_url,
+                     '--output', temp_filename ])
+        self._Call([ 'mv', temp_filename, dest_filename ])
+
     # Rebaseline a single file.
     def _RebaselineOneFile(self, expectations_subdir, builder_name,
                            infilename, outfilename):
         url = ('http://skia-autogen.googlecode.com/svn/gm-actual/' +
                expectations_subdir + '/' + builder_name + '/' +
                expectations_subdir + '/' + infilename)
-        cmd = [ 'curl', '--fail', '--silent', url ]
-        temp = tempfile.NamedTemporaryFile()
-        ret = self._Call(cmd, stdout=temp)
-        if ret != 0:
+
+        # Try to download this file, but if that fails, keep going...
+        #
+        # This not treated as a fatal failure because not all
+        # platforms generate all configs (e.g., Android does not
+        # generate PDF).
+        #
+        # We could tweak the list of configs within this tool to
+        # reflect which combinations the bots actually generate, and
+        # then fail if any of those expected combinations are
+        # missing... but then this tool would become useless every
+        # time someone tweaked the configs on the bots without
+        # updating this script.
+        try:
+            self._DownloadFile(source_url=url, dest_filename=outfilename)
+        except CommandFailedException:
             print '# Couldn\'t fetch ' + url
             return
-        cmd = [ 'cp', temp.name, outfilename ]
-        self._Call(cmd);
+
+        # Add this file to version control (if it isn't already).
         if self._is_svn_checkout:
             cmd = [ 'svn', 'add', '--quiet', outfilename ]
             self._Call(cmd)