Stop overriding log output in plugin.Serve in tests.

When testing, we don't want to override where log output gets sent--the
test framework takes care of that itself. go-plugin has disabled its use
of log.SetOutput for us, but #639 introduced a log.SetOutput in
plugin.Serve. This adds a plugin.ServeOpt property to disable that
log.SetOutput call so we can finally have tests where log lines don't
randomly show up in test output.

helper/resource/plugin.go

@@ -85,6 +85,7 @@ func runProviderCommand(t testing.T, f func() error, wd *plugintest.WorkingDir,
 				Level:  hclog.Trace,
 				Output: ioutil.Discard,
 			}),
+			NoLogOutputOverride: true,
 		}
 
 		// let's actually start the provider server
@@ -160,6 +161,7 @@ func runProviderCommand(t testing.T, f func() error, wd *plugintest.WorkingDir,
 				Level:  hclog.Trace,
 				Output: ioutil.Discard,
 			}),
+			NoLogOutputOverride: true,
 		}
 
 		// let's actually start the provider server

plugin/serve.go

@@ -45,23 +45,30 @@ type ServeOpts struct {
 	// plugin's lifecycle and communicate connection information. See the
 	// go-plugin GoDoc for more information.
 	TestConfig *plugin.ServeTestConfig
+
+	// Set NoLogOutputOverride to not override the log output with an hclog
+	// adapter. This should only be used when running the plugin in
+	// acceptance tests.
+	NoLogOutputOverride bool
 }
 
 // Serve serves a plugin. This function never returns and should be the final
 // function called in the main function of the plugin.
 func Serve(opts *ServeOpts) {
-	// In order to allow go-plugin to correctly pass log-levels through to
-	// terraform, we need to use an hclog.Logger with JSON output. We can
-	// inject this into the std `log` package here, so existing providers will
-	// make use of it automatically.
-	logger := hclog.New(&hclog.LoggerOptions{
-		// We send all output to terraform. Go-plugin will take the output and
-		// pass it through another hclog.Logger on the client side where it can
-		// be filtered.
-		Level:      hclog.Trace,
-		JSONFormat: true,
-	})
-	log.SetOutput(logger.StandardWriter(&hclog.StandardLoggerOptions{InferLevels: true}))
+	if !opts.NoLogOutputOverride {
+		// In order to allow go-plugin to correctly pass log-levels through to
+		// terraform, we need to use an hclog.Logger with JSON output. We can
+		// inject this into the std `log` package here, so existing providers will
+		// make use of it automatically.
+		logger := hclog.New(&hclog.LoggerOptions{
+			// We send all output to terraform. Go-plugin will take the output and
+			// pass it through another hclog.Logger on the client side where it can
+			// be filtered.
+			Level:      hclog.Trace,
+			JSONFormat: true,
+		})
+		log.SetOutput(logger.StandardWriter(&hclog.StandardLoggerOptions{InferLevels: true}))
+	}
 
 	// since the plugins may not yet be aware of the new protocol, we
 	// automatically wrap the plugins in the grpc shims.