[rubygems/rubygems] Add test cases from SHA1 RFC and improve test failure message

I found that the current test cases did not cover the bitwise AND
performed on modified words after each iteration
(7e5765a66c/bundler/lib/bundler/digest.rb (L50))

https://github.com/rubygems/rubygems/commit/c8de819fee

spec/bundler/bundler/digest_spec.rb

@@ -9,8 +9,15 @@ RSpec.describe Bundler::Digest do
     let(:stdlib) { ::Digest::SHA1 }
 
     it "is compatible with stdlib" do
-      ["foo", "skfjsdlkfjsdf", "3924m", "ldskfj"].each do |payload|
-        expect(subject.sha1(payload)).to be == stdlib.hexdigest(payload)
+      random_strings = ["foo", "skfjsdlkfjsdf", "3924m", "ldskfj"]
+
+      # https://datatracker.ietf.org/doc/html/rfc3174#section-7.3
+      rfc3174_test_cases = ["abc", "abcdbcdecdefdefgefghfghighijhijkijkljklmklmnlmnomnopnopq", "a", "01234567" * 8]
+
+      (random_strings + rfc3174_test_cases).each do |payload|
+        sha1 = subject.sha1(payload)
+        sha1_stdlib = stdlib.hexdigest(payload)
+        expect(sha1).to be == sha1_stdlib, "#{payload}'s sha1 digest (#{sha1}) did not match stlib's result (#{sha1_stdlib})"
       end
     end
   end