tests: import: gem: Add test for unrecognized license identifiers.

Exercises the map in 4f78d33f0 where every license
string is unrecognized, so the resulting package should have
(license (list unknown-license! unknown-license!)).

* tests/import/gem.scm (test-gibberish-licenses-json): New fixture.
  ("gem->guix-package with gibberish license identifiers"): New test.

Change-Id: I85cbb0574f9393749a84f4cf5818d4c1083a8476
Reviewed-by: Carlo Zancanaro <carlo@zancanaro.id.au>
Signed-off-by: Nguyễn Gia Phong <cnx@loang.net>

tests/import/gem.scm

@@ -138,6 +138,19 @@
   \"licenses\": [\"Ruby\", \"BSD-2-Clause\"]
 }")
 
+(define test-gibberish-licenses-json
+  "{
+  \"name\": \"gibberish-license-gem\",
+  \"version\": \"1.0.0\",
+  \"sha\": \"f3676eafca9987cb5fe263df1edf2538bf6dafc712b30e17be3543a9680547a8\",
+  \"info\": \"A gem with gibberish licenses\",
+  \"homepage_uri\": \"https://example.com\",
+  \"dependencies\": {
+    \"runtime\": []
+  },
+  \"licenses\": [\"foo\", \"bar\"]
+}")
+
 (test-begin "gem")
 
 (test-assert "gem->guix-package"