tests: add tests for go/protoutil/duration (#14965)

Signed-off-by: Manik Rana <manikrana54@gmail.com>

go/protoutil/duration_test.go

@@ -26,7 +26,6 @@ import (
 )
 
 func TestDurationFromProto(t *testing.T) {
-	t.Parallel()
 
 	tests := []struct {
 		name      string
@@ -59,13 +58,32 @@ func TestDurationFromProto(t *testing.T) {
 			isOk:      true,
 			shouldErr: true,
 		},
+		{
+			name: "nanoseconds",
+			in: &vttime.Duration{
+				Seconds: 1,
+				Nanos:   500000000,
+			},
+			expected:  time.Second + 500*time.Millisecond,
+			isOk:      true,
+			shouldErr: false,
+		},
+		{
+			name: "out of range nanoseconds",
+			in: &vttime.Duration{
+				Seconds: -1,
+				Nanos:   500000000,
+			},
+			expected:  0,
+			isOk:      true,
+			shouldErr: true,
+		},
 	}
 
 	for _, tt := range tests {
 		tt := tt
 
 		t.Run(tt.name, func(t *testing.T) {
-			t.Parallel()
 
 			actual, ok, err := DurationFromProto(tt.in)
 			if tt.shouldErr {
@@ -80,3 +98,38 @@ func TestDurationFromProto(t *testing.T) {
 		})
 	}
 }
+
+func TestDurationToProto(t *testing.T) {
+
+	tests := []struct {
+		name     string
+		in       time.Duration
+		expected *vttime.Duration
+	}{
+		{
+			name:     "success",
+			in:       time.Second * 1000,
+			expected: &vttime.Duration{Seconds: 1000},
+		},
+		{
+			name:     "zero duration",
+			in:       0,
+			expected: &vttime.Duration{},
+		},
+		{
+			name:     "nanoseconds",
+			in:       time.Second + 500*time.Millisecond,
+			expected: &vttime.Duration{Seconds: 1, Nanos: 500000000},
+		},
+	}
+
+	for _, tt := range tests {
+		tt := tt
+
+		t.Run(tt.name, func(t *testing.T) {
+
+			actual := DurationToProto(tt.in)
+			assert.Equal(t, tt.expected, actual)
+		})
+	}
+}