diff --git a/.simplecov b/.simplecov
new file mode 100644
index 0000000..61a52c0
--- /dev/null
+++ b/.simplecov
@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+require 'digest'
+
+digest = Digest::MD5.new
+digest.update('test')
+digest.update(ENV.fetch('BUNDLE_GEMFILE', 'gemfile')) if ENV['APPRAISAL_INITIALIZED']
+
+ENV['ENABLE_COVERAGE'] ||= '1'
+
+if ENV['ENABLE_COVERAGE'].to_i.positive?
+  SimpleCov.command_name(ENV['SIMPLECOV_COMMAND_NAME'] || digest.hexdigest)
+
+  # Hook Process._fork so forked children store their own coverage slice.
+  SimpleCov.merge_subprocesses true
+
+  SimpleCov.start do
+    merging true
+    add_filter %r{^/test/}
+  end
+end
diff --git a/Gemfile b/Gemfile
index 12cceea..6216c1a 100644
--- a/Gemfile
+++ b/Gemfile
@@ -17,7 +17,7 @@ group :test do
   gem 'rubocop-performance', '~> 1.26.0'
   gem 'rubocop-rake', '~> 0.7.1'
   gem 'rubocop-rspec', '~> 3.10.0'
-  gem 'simplecov', '~> 0.22.0'
+  gem 'simplecov', '~> 1.0.0'
   gem 'yard', '~> 0.9.44'
   if RUBY_VERSION >= '3.4'
     gem 'base64'
diff --git a/test/test_helper.rb b/test/test_helper.rb
index 1d22d12..6c5fa89 100644
--- a/test/test_helper.rb
+++ b/test/test_helper.rb
@@ -5,8 +5,6 @@
 # SPDX-License-Identifier: Apache-2.0
 
 require 'simplecov'
-SimpleCov.start
-
 require 'rake'
 require 'minitest'
 require 'minitest/autorun'
@@ -44,7 +42,6 @@ def run_in_subprocess(env_vars = {}, opts = {})
   read_pipe, write_pipe = IO.pipe
 
   pid = fork do
-    SimpleCov.command_name "subprocess-#{Process.pid}"
     read_pipe.close
     env_vars.each { |key, value| ENV[key] = value }
     ENV['OTEL_RUBY_REQUIRE_BUNDLER'] = 'false'
@@ -149,10 +146,7 @@ def run_in_subprocess(env_vars = {}, opts = {})
     ensure
       $stderr = old_stderr if defined?(old_stderr)
       write_pipe.close
-
-      # Store the simplecov result for this process
-      SimpleCov::ResultMerger.store_result(SimpleCov::Result.new(Coverage.result)) if SimpleCov.running
-      exit!(0)
+      exit(0)
     end
   end