diff --git a/pkg/document/crdt/counter_test.go b/pkg/document/crdt/counter_test.go
index de3345dfb..bc05d717a 100644
--- a/pkg/document/crdt/counter_test.go
+++ b/pkg/document/crdt/counter_test.go
@@ -30,44 +30,55 @@ import (
 
 func TestCounter(t *testing.T) {
 	t.Run("new counter test", func(t *testing.T) {
-		intCntWithInt32Value := crdt.NewCounter(crdt.IntegerCnt, int32(math.MaxInt32), time.InitialTicket)
+		intCntWithInt32Value, err := crdt.NewCounter(crdt.IntegerCnt, int32(math.MaxInt32), time.InitialTicket)
+		assert.NoError(t, err)
 		assert.Equal(t, crdt.IntegerCnt, intCntWithInt32Value.ValueType())
 
-		intCntWithInt64Value := crdt.NewCounter(crdt.IntegerCnt, int64(math.MaxInt32+1), time.InitialTicket)
+		intCntWithInt64Value, err := crdt.NewCounter(crdt.IntegerCnt, int64(math.MaxInt32+1), time.InitialTicket)
+		assert.NoError(t, err)
 		assert.Equal(t, crdt.IntegerCnt, intCntWithInt64Value.ValueType())
 
-		intCntWithIntValue := crdt.NewCounter(crdt.IntegerCnt, math.MaxInt32, time.InitialTicket)
+		intCntWithIntValue, err := crdt.NewCounter(crdt.IntegerCnt, math.MaxInt32, time.InitialTicket)
+		assert.NoError(t, err)
 		assert.Equal(t, crdt.IntegerCnt, intCntWithIntValue.ValueType())
 
-		intCntWithDoubleValue := crdt.NewCounter(crdt.IntegerCnt, 0.5, time.InitialTicket)
+		intCntWithDoubleValue, err := crdt.NewCounter(crdt.IntegerCnt, 0.5, time.InitialTicket)
+		assert.NoError(t, err)
 		assert.Equal(t, crdt.IntegerCnt, intCntWithDoubleValue.ValueType())
 
-		intCntWithUnsupportedValue := func() { crdt.NewCounter(crdt.IntegerCnt, "", time.InitialTicket) }
-		assert.Panics(t, intCntWithUnsupportedValue)
+		_, err = crdt.NewCounter(crdt.IntegerCnt, "", time.InitialTicket)
+		assert.EqualError(t, err, "unsupported type")
 
-		longCntWithInt32Value := crdt.NewCounter(crdt.LongCnt, int32(math.MaxInt32), time.InitialTicket)
+		longCntWithInt32Value, err := crdt.NewCounter(crdt.LongCnt, int32(math.MaxInt32), time.InitialTicket)
+		assert.NoError(t, err)
 		assert.Equal(t, crdt.LongCnt, longCntWithInt32Value.ValueType())
 
-		longCntWithInt64Value := crdt.NewCounter(crdt.LongCnt, int64(math.MaxInt32+1), time.InitialTicket)
+		longCntWithInt64Value, err := crdt.NewCounter(crdt.LongCnt, int64(math.MaxInt32+1), time.InitialTicket)
+		assert.NoError(t, err)
 		assert.Equal(t, crdt.LongCnt, longCntWithInt64Value.ValueType())
 
-		longCntWithIntValue := crdt.NewCounter(crdt.LongCnt, math.MaxInt32+1, time.InitialTicket)
+		longCntWithIntValue, err := crdt.NewCounter(crdt.LongCnt, math.MaxInt32+1, time.InitialTicket)
+		assert.NoError(t, err)
 		assert.Equal(t, crdt.LongCnt, longCntWithIntValue.ValueType())
 
-		longCntWithDoubleValue := crdt.NewCounter(crdt.LongCnt, 0.5, time.InitialTicket)
+		longCntWithDoubleValue, err := crdt.NewCounter(crdt.LongCnt, 0.5, time.InitialTicket)
+		assert.NoError(t, err)
 		assert.Equal(t, crdt.LongCnt, longCntWithDoubleValue.ValueType())
 
-		longCntWithUnsupportedValue := func() { crdt.NewCounter(crdt.LongCnt, "", time.InitialTicket) }
-		assert.Panics(t, longCntWithUnsupportedValue)
+		_, err = crdt.NewCounter(crdt.LongCnt, "", time.InitialTicket)
+		assert.EqualError(t, err, "unsupported type")
 	})
 
 	t.Run("increase test", func(t *testing.T) {
 		var x = 5
 		var y int64 = 10
 		var z = 3.14
-		integer := crdt.NewCounter(crdt.IntegerCnt, x, time.InitialTicket)
-		long := crdt.NewCounter(crdt.LongCnt, y, time.InitialTicket)
-		double := crdt.NewCounter(crdt.IntegerCnt, z, time.InitialTicket)
+		integer, err := crdt.NewCounter(crdt.IntegerCnt, x, time.InitialTicket)
+		assert.NoError(t, err)
+		long, err := crdt.NewCounter(crdt.LongCnt, y, time.InitialTicket)
+		assert.NoError(t, err)
+		double, err := crdt.NewCounter(crdt.IntegerCnt, z, time.InitialTicket)
+		assert.NoError(t, err)
 
 		integerOperand := crdt.NewPrimitive(x, time.InitialTicket)
 		longOperand := crdt.NewPrimitive(y, time.InitialTicket)
@@ -90,21 +101,14 @@ func TestCounter(t *testing.T) {
 		assert.Equal(t, double.Marshal(), "21")
 
 		// error process test
-		// TODO: it should be modified to error check
-		// when 'Remove panic from server code (#50)' is completed.
-		unsupportedTypePanicTest := func() {
-			r := recover()
-			assert.NotNil(t, r)
-			assert.Equal(t, r, "unsupported type")
+		unsupportedTypeErrorTest := func(v interface{}) {
+			_, err = crdt.NewCounter(crdt.IntegerCnt, v, time.InitialTicket)
+			assert.EqualError(t, err, "unsupported type")
 		}
-		unsupportedTest := func(v interface{}) {
-			defer unsupportedTypePanicTest()
-			crdt.NewCounter(crdt.IntegerCnt, v, time.InitialTicket)
-		}
-		unsupportedTest("str")
-		unsupportedTest(true)
-		unsupportedTest([]byte{2})
-		unsupportedTest(gotime.Now())
+		unsupportedTypeErrorTest("str")
+		unsupportedTypeErrorTest(true)
+		unsupportedTypeErrorTest([]byte{2})
+		unsupportedTypeErrorTest(gotime.Now())
 
 		assert.Equal(t, integer.Marshal(), "23")
 		assert.Equal(t, long.Marshal(), "28")
@@ -112,7 +116,8 @@ func TestCounter(t *testing.T) {
 	})
 
 	t.Run("Counter value overflow test", func(t *testing.T) {
-		integer := crdt.NewCounter(crdt.IntegerCnt, math.MaxInt32, time.InitialTicket)
+		integer, err := crdt.NewCounter(crdt.IntegerCnt, math.MaxInt32, time.InitialTicket)
+		assert.NoError(t, err)
 		assert.Equal(t, integer.ValueType(), crdt.IntegerCnt)
 
 		operand := crdt.NewPrimitive(1, time.InitialTicket)