module SimpleCov::LastRun

def last_run_path 

def last_run_path
  File.join(SimpleCov.coverage_path, ".last_run.json")
end

def read 

def read
  return nil unless File.exist?(last_run_path)
  json = File.read(last_run_path)
  return nil if json.strip.empty?
  JSON.parse(json, symbolize_names: true)
end

def write(json)

MaximumCoverageDrop) never sees a half-written file.
concurrent reader (e.g. another parallel-tests worker checking
Write to a process-private temp file, then atomically rename, so a 
def write(json)
  FileUtils.mkdir_p(SimpleCov.coverage_path)
  temp_path = "#{last_run_path}.#{Process.pid}.tmp"
  File.open(temp_path, "w") { |f| f.puts JSON.pretty_generate(json) }
  File.rename(temp_path, last_run_path)
end