add more tests

connector/api/decimal.go

@@ -20,7 +20,7 @@ type Decimal struct {
 func NewDecimal[T comparable](value T) (Decimal, error) {
 	result := Decimal{}
 	if err := result.FromValue(value); err != nil {
-		return Decimal{}, nil
+		return Decimal{}, err
 	}
 	return result, nil
 }
@@ -50,7 +50,7 @@ func (bi Decimal) MarshalJSON() ([]byte, error) {
 func (bi *Decimal) UnmarshalJSON(b []byte) error {
 	var value any
 	if err := json.Unmarshal(b, &value); err != nil {
-		return err
+		return fmt.Errorf("invalid decimal value: %s", err)
 	}
 
 	return bi.FromValue(value)

connector/api/decimal_test.go

@@ -0,0 +1,30 @@
+package api
+
+import (
+	"encoding/json"
+	"testing"
+
+	"github.com/hasura/ndc-sdk-go/utils"
+	"gotest.tools/v3/assert"
+)
+
+func TestDecimal(t *testing.T) {
+	assert.Assert(t, Decimal{}.IsNil())
+	assert.Equal(t, Decimal{}.String(), "Inf")
+	assert.Equal(t, Decimal{value: utils.ToPtr(1.2)}.String(), "1.2")
+
+	_, err := NewDecimal("foo")
+	assert.ErrorContains(t, err, "failed to convert Float, got: foo")
+
+	dec, err := NewDecimal("1.1")
+	assert.NilError(t, err)
+	assert.Equal(t, dec.ScalarName(), "Decimal")
+	assert.Equal(t, dec.String(), "1.1")
+
+	assert.ErrorContains(t, json.Unmarshal([]byte("foo"), &dec), "invalid character")
+	assert.NilError(t, json.Unmarshal([]byte("2.2"), &dec))
+
+	bs, err := json.Marshal(dec)
+	assert.NilError(t, err)
+	assert.Equal(t, string(bs), `"2.2"`)
+}