Update add3prf.py

Change the license detection logic to return if a dual-license was
found. Update the metadata comment as discussed in b/179902335.
Add unit tests for add_module_license and decide_license_type.

Bug: 179902335
Test: atest --host add3prf_test; manually run add3prf.py in {ahash,
  libloading, parking_lot, ring}
Change-Id: I3184b5cf0955d124170b9e5987308507bdef6e9a

scripts/add3prf_test.py

@@ -0,0 +1,76 @@
+# Copyright 2021 Google Inc. All rights reserved.
+#
+# 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 unittest
+
+from pyfakefs import fake_filesystem_unittest
+
+import add3prf
+
+class LicenseDetectionTestCase(fake_filesystem_unittest.TestCase):
+
+  def setUp(self):
+    self.setUpPyfakefs()
+
+  def test_dual_license(self):
+    self.fs.create_file("LICENSE-APACHE")
+    self.fs.create_file("LICENSE-MIT")
+    licenses = add3prf.decide_license_type("MIT OR Apache-2.0")
+    self.assertEqual(len(licenses), 2)
+    preferred_license = licenses[0]
+    self.assertEqual(preferred_license.type, add3prf.LicenseType.APACHE2)
+    self.assertEqual(preferred_license.filename, "LICENSE-APACHE")
+
+  def test_mit_license(self):
+    self.fs.create_file("LICENSE")
+    licenses = add3prf.decide_license_type("MIT")
+    self.assertEqual(len(licenses), 1)
+    preferred_license = licenses[0]
+    self.assertEqual(preferred_license.type, add3prf.LicenseType.MIT)
+    self.assertEqual(preferred_license.filename, "LICENSE")
+
+  def test_misc_license(self):
+    self.fs.create_file("LICENSE.txt")
+    licenses = add3prf.decide_license_type("")
+    self.assertEqual(len(licenses), 1)
+    preferred_license = licenses[0]
+    self.assertEqual(preferred_license.type, add3prf.LicenseType.BSD_LIKE)
+    self.assertEqual(preferred_license.filename, "LICENSE.txt")
+
+  def test_missing_license_file(self):
+    with self.assertRaises(FileNotFoundError):
+      add3prf.decide_license_type("MIT OR Apache-2.0")
+
+
+class AddModuleLicenseTestCase(fake_filesystem_unittest.TestCase):
+
+  def setUp(self):
+    self.setUpPyfakefs()
+
+  def test_no_file(self):
+    add3prf.add_module_license(add3prf.LicenseType.APACHE2)
+    self.assertTrue(os.path.exists("MODULE_LICENSE_APACHE2"))
+
+  def test_already_exists(self):
+    self.fs.create_file("MODULE_LICENSE_APACHE2")
+    add3prf.add_module_license(add3prf.LicenseType.APACHE2)
+
+  def test_mit_apache(self):
+    self.fs.create_file("MODULE_LICENSE_MIT")
+    with self.assertRaises(Exception):
+      add3prf.add_module_license(add3prf.LicenseType.APACHE2)
+
+
+if __name__ == '__main__':
+  unittest.main(verbosity=2)