Improve specs and error messages in extendable config

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

@@ -50,7 +50,7 @@ module Gitlab
 
             if unknown_extension?
               raise Entry::InvalidExtensionError,
-                    "#{key}: unknown `extends` key"
+                    "#{key}: unknown key in `extends`"
             end
 
             if invalid_base?
@@ -60,7 +60,7 @@ module Gitlab
 
             if nesting_too_deep?
               raise Entry::NestingTooDeepError,
-                    "#{key}: `extends` nesting too deep"
+                    "#{key}: nesting too deep in `extends`"
             end
 
             if circular_dependency?

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

@@ -139,7 +139,7 @@ describe Gitlab::Ci::Config::Extendable::Entry do
       it 'raises an error' do
         expect { subject.extend! }
           .to raise_error(described_class::InvalidExtensionError,
-                          /unknown `extends` key/)
+                          /unknown key/)
       end
     end
 

spec/lib/gitlab/ci/config/extendable_spec.rb

@@ -80,9 +80,19 @@ describe Gitlab::Ci::Config::Extendable do
             only: { refs: %w[master] }
           },
 
+          build: {
+            extends: 'something',
+            stage: 'build'
+          },
+
+          deploy: {
+            stage: 'deploy',
+            extends: '.first'
+          },
+
           something: {
             extends: '.first',
-            script: 'deploy',
+            script: 'exec',
             only: { variables: %w[$SOMETHING] }
           },
 
@@ -102,7 +112,24 @@ describe Gitlab::Ci::Config::Extendable do
 
           something: {
             extends: '.first',
-            script: 'deploy',
+            script: 'exec',
+            only: {
+              kubernetes: 'active',
+              variables: %w[$SOMETHING]
+            }
+          },
+
+          deploy: {
+            script: 'run',
+            stage: 'deploy',
+            only: { kubernetes: 'active' },
+            extends: '.first'
+          },
+
+          build: {
+            extends: 'something',
+            script: 'exec',
+            stage: 'build',
             only: {
               kubernetes: 'active',
               variables: %w[$SOMETHING]

spec/lib/gitlab/ci/yaml_processor_spec.rb

@@ -1367,7 +1367,7 @@ module Gitlab
 
           expect { Gitlab::Ci::YamlProcessor.new(config) }
             .to raise_error(Gitlab::Ci::YamlProcessor::ValidationError,
-                            'rspec: unknown `extends` key')
+                            'rspec: unknown key in `extends`')
         end
       end