Ensure the log line attributes take priority

This commit does not change the implementation, which already did
this, but writes a test to ensure this behaviour and specifies it
in the changelog.

.changesets/add-default-attributes-to-logger.md

@@ -3,4 +3,10 @@ bump: patch
 type: add
 ---
 
-Add default attributes to Logger
+Allow for default attributes to be given when initialising a `Logger` instance:
+
+```ruby
+order_logger = Appsignal::Logger.new("app", attributes: { order_id: 123 })
+```
+
+All log lines reported by this logger will contain the given attribute. Attributes given when reporting the log line will be merged with the default attributes for the logger, with those in the log line taking priority.

spec/lib/appsignal/logger_spec.rb

@@ -201,6 +201,15 @@
       expect(default_attributes).to eq({ :some_key => "some_value" })
       expect(line_attributes).to eq({ :other_key => "other_value" })
     end
+
+    it "prioritises line attributes over default attributes" do
+      logger = Appsignal::Logger.new("group", :attributes => { :some_key => "some_value" })
+
+      expect(Appsignal::Extension).to receive(:log).with("group", 6, 0, "Some message",
+        Appsignal::Utils::Data.generate({ :some_key => "other_value" }))
+
+      logger.error("Some message", { :some_key => "other_value" })
+    end
   end
 
   describe "#error with exception object" do