Add spec and CHANGELOG

CHANGELOG.md

@@ -19,6 +19,10 @@ To install release candidates run `[sudo] gem install cocoapods --pre`
 
 ##### Bug Fixes
 
+* Improve repo lint error message when no repo found with given name.  
+  [Muhammed Yavuz Nuzumlalı](https://github.com/manuyavuz)
+  [#4142](https://github.com/CocoaPods/CocoaPods/issues/4142)
+
 * Fix a crash in dependency resolution when running Ruby 2.3.  
   [Samuel Giddins](https://github.com/segiddins)
   [#4345](https://github.com/CocoaPods/CocoaPods/issues/4345)

spec/functional/command/repo/lint_spec.rb

@@ -16,5 +16,12 @@ module Pod
       repo = fixture('spec-repos/test_repo').to_s
       lambda { run_command('repo', 'lint', repo) }.should.not.raise
     end
+
+    it 'raises when there is no repository with given name' do
+      repo = fixture('spec-repos/not_existing_repo').to_s
+      e = lambda { run_command('repo', 'lint', repo) }.should.raise Informative
+      e.message.should.match(/Unable to find a source named/)
+      e.message.should.match(/not_existing_repo/)
+    end
   end
 end