releasetools: Add sanity test for sign_apex.

This ensures a matching interface between sign_apex and apex_utils.

The test apex `testdata/foo.apex` is generated by running
`system/apex/apexer/runtests.sh`.

Test: python -m unittest test_sign_apex
Test: atest releasetools_test
Change-Id: I7c14b1df2a3038ad206aa3e5aac084c47baaa00b
diff --git a/tools/releasetools/test_sign_apex.py b/tools/releasetools/test_sign_apex.py
new file mode 100644
index 0000000..4dcc214
--- /dev/null
+++ b/tools/releasetools/test_sign_apex.py
@@ -0,0 +1,41 @@
+#
+# Copyright (C) 2019 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+
+import os.path
+
+import common
+import sign_apex
+import test_utils
+
+
+class SignApexTest(test_utils.ReleaseToolsTestCase):
+
+  def setUp(self):
+    self.testdata_dir = test_utils.get_testdata_dir()
+    self.assertTrue(os.path.exists(self.testdata_dir))
+
+    common.OPTIONS.search_path = test_utils.get_search_path()
+
+  @test_utils.SkipIfExternalToolsUnavailable()
+  def test_SignApexFile(self):
+    foo_apex = os.path.join(self.testdata_dir, 'foo.apex')
+    payload_key = os.path.join(self.testdata_dir, 'testkey_RSA4096.key')
+    container_key = os.path.join(self.testdata_dir, 'testkey')
+    signed_foo_apex = sign_apex.SignApexFile(
+        foo_apex,
+        payload_key,
+        container_key)
+    self.assertTrue(os.path.exists(signed_foo_apex))