Marshaling & Unmarshaling time return initial value

There was a lack of symmetry that would prevent times for being
symmetrical. That is because time.Parse actually parses an RFC3339Nano
implicitly, thereby allowing nanosecond resolution on unmarshaling a
time. Therefore we now marshal into nanoseconds, getting more
information into GraphQL times when querying for a time, and restoring
the symmetry

graphql/time.go

@@ -13,7 +13,7 @@ func MarshalTime(t time.Time) Marshaler {
 	}
 
 	return WriterFunc(func(w io.Writer) {
-		io.WriteString(w, strconv.Quote(t.Format(time.RFC3339)))
+		io.WriteString(w, strconv.Quote(t.Format(time.RFC3339Nano)))
 	})
 }
 

graphql/time_test.go

@@ -0,0 +1,25 @@
+package graphql
+
+import (
+	"bytes"
+	"strconv"
+	"testing"
+	"time"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestTime(t *testing.T) {
+	t.Run("symmetry", func(t *testing.T) {
+		initialTime := time.Now()
+		buf := bytes.NewBuffer([]byte{})
+		MarshalTime(initialTime).MarshalGQL(buf)
+
+		str, err := strconv.Unquote(buf.String())
+		require.Nil(t, err)
+		newTime, err := UnmarshalTime(str)
+		require.Nil(t, err)
+
+		require.True(t, initialTime.Equal(newTime), "expected times %v and %v to equal", initialTime, newTime)
+	})
+}