Add unlicense support to add3prf.py

This adds the ability to detect and generate the correct METADATA file
for unlicense licensed crates.

Bug: 317361040
Test: atest --host add3prf_test; Ran against https://crates.io/crates/aho-corasick
Change-Id: Icbed2fbab7368f5faef2194a4836c369b038979c
diff --git a/scripts/add3prf_test.py b/scripts/add3prf_test.py
index 80bcfa4..32d5c7a 100755
--- a/scripts/add3prf_test.py
+++ b/scripts/add3prf_test.py
@@ -82,6 +82,24 @@
     self.assertEqual(preferred_license.group, add3prf.LicenseGroup.PERMISSIVE)
     self.assertEqual(preferred_license.filename, "LICENSE-0BSD")
 
+  def test_unlicense_license(self):
+    self.fs.create_file("LICENSE")
+    licenses = add3prf.decide_license_type("Unlicense")
+    self.assertEqual(len(licenses), 1)
+    preferred_license = licenses[0]
+    self.assertEqual(preferred_license.type, add3prf.LicenseType.UNLICENSE)
+    self.assertEqual(preferred_license.group, add3prf.LicenseGroup.PERMISSIVE)
+    self.assertEqual(preferred_license.filename, "LICENSE")
+
+  def test_unlicense_licensefile(self):
+    self.fs.create_file("UNLICENSE")
+    licenses = add3prf.decide_license_type("")
+    self.assertEqual(len(licenses), 1)
+    preferred_license = licenses[0]
+    self.assertEqual(preferred_license.type, add3prf.LicenseType.UNLICENSE)
+    self.assertEqual(preferred_license.group, add3prf.LicenseGroup.PERMISSIVE)
+    self.assertEqual(preferred_license.filename, "UNLICENSE")
+
 
 class AddModuleLicenseTestCase(fake_filesystem_unittest.TestCase):