Don't call SimpleCov.result before checking SimpleCov.result? (#674)

* simplecov.rb: check .result? in .run_exit_tasks! rather than in .process_result
in order to avoid instantiating SimpleCov.result prior to performing the .result? check, as doing so guarantees that .result? will always return 'true'

* spec/result_merger_spec.rb: test that manually-stored merged results data isn't clobbered by SimpleCov.run_exit_tasks\!/.process_results

lib/simplecov.rb

@@ -199,7 +199,9 @@ def run_exit_tasks!
 
       SimpleCov.at_exit.call
 
-      exit_status = SimpleCov.process_result(SimpleCov.result, exit_status)
+      # Don't modify the exit status unless the result has already been
+      # computed
+      exit_status = SimpleCov.process_result(SimpleCov.result, exit_status) if SimpleCov.result?
 
       # Force exit with stored status (see github issue #5)
       # unless it's nil or 0 (see github issue #281)
@@ -212,7 +214,6 @@ def run_exit_tasks!
     #   exit_status = SimpleCov.process_result(SimpleCov.result, exit_status)
     #
     def process_result(result, exit_status)
-      return exit_status unless SimpleCov.result? # Result has been computed
       return exit_status if exit_status != SimpleCov::ExitCodes::SUCCESS # Existing errors
 
       covered_percent = result.covered_percent.round(2)

spec/result_merger_spec.rb

@@ -104,6 +104,31 @@
         expect(SimpleCov::ResultMerger).to receive(:synchronize_resultset)
         SimpleCov::ResultMerger.store_result({})
       end
+
+      it "persists after exit" do
+        skip "fork not available on JRuby" if RUBY_ENGINE == "jruby"
+
+        coverage = {__FILE__ => 5.downto(1).to_a}
+
+        # Fork to ensure that the Kernel.at_exit block defined in
+        # simplecov/defaults.rb runs
+        pid = Kernel.fork do
+          SimpleCov.start
+
+          # Override the default SimpleCov.at_exit block to avoid instantiating
+          # SimpleCov.result
+          SimpleCov.at_exit {}
+          SimpleCov.command_name "merged result persistence"
+
+          result = SimpleCov::Result.new(coverage)
+          SimpleCov::ResultMerger.store_result(result)
+        end
+
+        Process.waitpid pid
+
+        merged_result = SimpleCov::ResultMerger.merged_result
+        expect(merged_result.original_result).to include(coverage)
+      end
     end
 
     describe ".resultset" do