Alerting: Add QueryError to expr package (#41737)

pkg/expr/nodes_test.go

@@ -0,0 +1,16 @@
+package expr
+
+import (
+	"errors"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+func TestQueryError(t *testing.T) {
+	e := QueryError{
+		RefID: "A",
+		Err:   errors.New("this is an error message"),
+	}
+	assert.EqualError(t, e, "failed to execute query A: this is an error message")
+}