[Bugfix] apm.DefaultTracer misbehaves when transport configuration is invalid

tracer.go

@@ -53,10 +53,8 @@ var (
 // DefaultTracer returns the default global Tracer, set the first time the
 // function is called, or after calling SetDefaultTracer(nil).
 //
-// The default tracer is configured via environment variables, and will always
-// be non-nil. If any of the environment variables are invalid, the
-// corresponding errors will be logged to stderr and the default values will be
-// used instead.
+// The default tracer is configured via environment variables, and if the those are invalid
+// the tracer will be disabled.
 func DefaultTracer() *Tracer {
 	tracerMu.RLock()
 	if defaultTracer != nil {
@@ -314,7 +312,7 @@ func (opts *TracerOptions) initDefaults(continueOnError bool) error {
 	if opts.Transport == nil {
 		initialTransport, err := initialTransport(opts.ServiceName, opts.ServiceVersion)
 		if failed(err) {
-			opts.Transport = transport.NewDiscardTransport(err)
+			active = false
 		} else {
 			opts.Transport = initialTransport
 		}

tracer_test.go

@@ -593,21 +593,9 @@ func TestTracerDefaultTransport(t *testing.T) {
 		defer os.Unsetenv("ELASTIC_APM_SERVER_TIMEOUT")
 
 		// NewTracer returns errors.
-		tracer, err := apm.NewTracer("", "")
+		_, err := apm.NewTracer("", "")
 		require.Error(t, err)
 		assert.EqualError(t, err, "failed to parse ELASTIC_APM_SERVER_TIMEOUT: invalid duration never")
-
-		// Implicitly created Tracers will have a discard tracer.
-		apm.SetDefaultTracer(nil)
-		tracer = apm.DefaultTracer()
-
-		tracer.StartTransaction("name", "type").End()
-		tracer.Flush(nil)
-		assert.Equal(t, apm.TracerStats{
-			Errors: apm.TracerStatsErrors{
-				SendStream: 1,
-			},
-		}, tracer.Stats())
 	})
 }