paycheck: move stuff from checker_unittest.py to test_utils.py

This is all stuff that'll come in handy when testing other modules.

BUG=chromium:217039,chromium:215780,chromium:189855
TEST=Passes unittests

Change-Id: I57d1fae97330f22748885f8028352f07b5058396
Reviewed-on: https://gerrit.chromium.org/gerrit/47615
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
diff --git a/scripts/update_payload/test_utils.py b/scripts/update_payload/test_utils.py
index d05aafd..6d455d5 100644
--- a/scripts/update_payload/test_utils.py
+++ b/scripts/update_payload/test_utils.py
@@ -18,6 +18,23 @@
   """An error during testing of update payload code."""
 
 
+# Private/public RSA keys used for testing.
+_PRIVKEY_FILE_NAME = 'payload-test-key.pem'
+_PUBKEY_FILE_NAME = 'payload-test-key.pub'
+
+
+def KiB(count):
+  return count << 10
+
+
+def MiB(count):
+  return count << 20
+
+
+def GiB(count):
+  return count << 30
+
+
 def _WriteInt(file_obj, size, is_unsigned, val):
   """Writes a binary-encoded integer to a file.