fix(alerting): fixes broken no_value evaluator

closes #6701

pkg/services/alerting/conditions/evaluator.go

@@ -17,9 +17,9 @@ type AlertEvaluator interface {
 	Eval(reducedValue null.Float) bool
 }
 
-type NoDataEvaluator struct{}
+type NoValueEvaluator struct{}
 
-func (e *NoDataEvaluator) Eval(reducedValue null.Float) bool {
+func (e *NoValueEvaluator) Eval(reducedValue null.Float) bool {
 	return reducedValue.Valid == false
 }
 
@@ -118,8 +118,8 @@ func NewAlertEvaluator(model *simplejson.Json) (AlertEvaluator, error) {
 		return newRangedEvaluator(typ, model)
 	}
 
-	if typ == "no_data" {
-		return &NoDataEvaluator{}, nil
+	if typ == "no_value" {
+		return &NoValueEvaluator{}, nil
 	}
 
 	return nil, alerting.ValidationError{Reason: "Evaluator invalid evaluator type: " + typ}

pkg/services/alerting/conditions/evaluator_test.go

@@ -44,15 +44,20 @@ func TestEvalutors(t *testing.T) {
 		So(evalutorScenario(`{"type": "outside_range", "params": [100, 1] }`, 50), ShouldBeFalse)
 	})
 
-	Convey("no_data", t, func() {
-		So(evalutorScenario(`{"type": "no_data", "params": [] }`, 50), ShouldBeFalse)
+	Convey("no_value", t, func() {
+		Convey("should be false if serie have values", func() {
+			So(evalutorScenario(`{"type": "no_value", "params": [] }`, 50), ShouldBeFalse)
+		})
 
-		jsonModel, err := simplejson.NewJson([]byte(`{"type": "no_data", "params": [] }`))
+		Convey("should be true when the serie have no value", func() {
+			jsonModel, err := simplejson.NewJson([]byte(`{"type": "no_value", "params": [] }`))
 			So(err, ShouldBeNil)
 
 			evaluator, err := NewAlertEvaluator(jsonModel)
 			So(err, ShouldBeNil)
 
 			So(evaluator.Eval(null.FloatFromPtr(nil)), ShouldBeTrue)
+
+		})
 	})
 }