Add coverage reporting with Codecov integration and badge

Co-authored-by: kwerle <23320+kwerle@users.noreply.github.com>

Author: Copilot

.github/workflows/test.yml

@@ -20,3 +20,11 @@ jobs:
     - uses: actions/checkout@v2
     - name: Run tests
       run: make test
+    - name: Run tests with coverage
+      run: make coverage
+    - name: Upload coverage to Codecov
+      uses: codecov/codecov-action@v4
+      with:
+        files: ./coverage/coverage.json
+        fail_ci_if_error: false
+        token: ${{ secrets.CODECOV_TOKEN }}

README.md

@@ -1,4 +1,5 @@
 ![Build Status](https://github.com/kwerle/ruby_language_server/actions/workflows/test.yml/badge.svg)
+[![codecov](https://codecov.io/gh/kwerle/ruby_language_server/branch/master/graph/badge.svg)](https://codecov.io/gh/kwerle/ruby_language_server)
 # Overview
 
 https://github.com/kwerle/ruby_language_server

spec/test_helper.rb

@@ -2,9 +2,12 @@
 
 if ENV['COVERAGE']
   require 'simplecov'
+  require 'simplecov_json_formatter'
   SimpleCov.start do
     add_filter '/spec/'
     add_filter '/vendor/'
+    # Use JSON formatter for CI/Codecov integration
+    formatter SimpleCov::Formatter::JSONFormatter if ENV['CI']
   end
 end