Improve extended CI/CD config specs and fix a bug

lib/gitlab/ci/config/extendable/collection.rb

@@ -10,7 +10,7 @@ module Gitlab
           CircularDependencyError = Class.new(ExtensionError)
 
           def initialize(hash)
-            @hash = hash.deep_dup
+            @hash = hash.to_h.deep_dup
 
             each { |entry| entry.extend! if entry.extensible? }
           end

lib/gitlab/ci/config/extendable/entry.rb

@@ -40,16 +40,17 @@ module Gitlab
 
             if unknown_extension?
               raise Extendable::Collection::InvalidExtensionError,
-                    'Unknown extension!'
+                    "Unknown extends key in extended `#{key}`!"
             end
 
             if invalid_base?
               raise Extendable::Collection::InvalidExtensionError,
-                    'Invalid base hash!'
+                    "Invalid base hash in extended `#{key}`!"
             end
 
             if circular_dependency?
-              raise Extendable::Collection::CircularDependencyError
+              raise Extendable::Collection::CircularDependencyError,
+                    "Circular dependency detected in extended `#{key}`!"
             end
 
             @context[key] = base_hash!.deep_merge(value)
@@ -62,7 +63,7 @@ module Gitlab
           end
 
           def unknown_extension?
-            !@context.key?(key)
+            !@context.key?(extends_key)
           end
 
           def invalid_base?

spec/lib/gitlab/ci/config/extendable/collection_spec.rb

@@ -179,7 +179,7 @@ describe Gitlab::Ci::Config::Extendable::Collection do
       end
     end
 
-    context 'when extensible entry has non-hash inheritace defined' do
+    context 'when extensible entry has non-hash inheritance defined' do
       let(:hash) do
         {
           test: {

spec/lib/gitlab/ci/config/extendable/entry_spec.rb

@@ -115,13 +115,13 @@ describe Gitlab::Ci::Config::Extendable::Entry do
       let(:hash) do
         {
           first: 'my value',
-          second: { extends: 'first' },
-          test: { extends: 'second' }
+          test: { extends: 'first' }
         }
       end
 
       it 'raises an error' do
-        expect { subject.extend! }.to raise_error(StandardError)
+        expect { subject.extend! }
+          .to raise_error(StandardError, /Invalid base hash/)
       end
     end
 
@@ -131,7 +131,8 @@ describe Gitlab::Ci::Config::Extendable::Entry do
       end
 
       it 'raises an error' do
-        expect { subject.extend! }.to raise_error(StandardError)
+        expect { subject.extend! }
+          .to raise_error(StandardError, /Unknown extends key/)
       end
     end
 
@@ -177,7 +178,7 @@ describe Gitlab::Ci::Config::Extendable::Entry do
       end
 
       it 'does not mutate orignal context' do
-        original = hash.dup
+        original = hash.deep_dup
 
         subject.extend!