Implement Stringer for service.State

Signed-off-by: Bogdan Drutu <bogdandrutu@gmail.com>

service/collector.go

@@ -50,6 +50,20 @@ const (
 	Closed
 )
 
+func (s State) String() string {
+	switch s {
+	case Starting:
+		return "Starting"
+	case Running:
+		return "Running"
+	case Closing:
+		return "Closing"
+	case Closed:
+		return "Closed"
+	}
+	return ""
+}
+
 // (Internal note) Collector Lifecycle:
 // - New constructs a new Collector.
 // - Run starts the collector.

service/collector_test.go

@@ -40,6 +40,13 @@ import (
 	"go.opentelemetry.io/collector/internal/testutil"
 )
 
+func TestStateString(t *testing.T) {
+	assert.Equal(t, "Starting", Starting.String())
+	assert.Equal(t, "Running", Running.String())
+	assert.Equal(t, "Closing", Closing.String())
+	assert.Equal(t, "Closed", Closed.String())
+}
+
 // TestCollector_StartAsGoRoutine must be the first unit test on the file,
 // to test for initialization without setting CLI flags.
 func TestCollector_StartAsGoRoutine(t *testing.T) {