fix(types): positive decimal from string must be finite (#1210)

* fix(types): positive decimal from string must be finite

* fix(types): positive decimal from string must be finite

* add godocs and test

* remove miscommit test files

* update test per review comment

types/math/dec.go

@@ -83,7 +83,7 @@ func NewPositiveDecFromString(s string) (Dec, error) {
 	if err != nil {
 		return Dec{}, ErrInvalidDecString.Wrap(err.Error())
 	}
-	if !d.IsPositive() {
+	if !d.IsPositive() || !d.IsFinite() {
 		return Dec{}, ErrInvalidDecString.Wrapf("expected a positive decimal, got %s", s)
 	}
 	return d, nil
@@ -246,18 +246,26 @@ func (x Dec) Equal(y Dec) bool {
 	return x.dec.Cmp(&y.dec) == 0
 }
 
+// IsZero returns true if the decimal is zero.
 func (x Dec) IsZero() bool {
 	return x.dec.IsZero()
 }
 
+// IsNegative returns true if the decimal is negative.
 func (x Dec) IsNegative() bool {
 	return x.dec.Negative && !x.dec.IsZero()
 }
 
+// IsPositive returns true if the decimal is positive.
 func (x Dec) IsPositive() bool {
 	return !x.dec.Negative && !x.dec.IsZero()
 }
 
+// IsFinite returns true if the decimal is finite.
+func (x Dec) IsFinite() bool {
+	return x.dec.Form == apd.Finite
+}
+
 // NumDecimalPlaces returns the number of decimal places in x.
 func (x Dec) NumDecimalPlaces() uint32 {
 	exp := x.dec.Exponent

types/math/dec_test.go

@@ -598,6 +598,18 @@ func floatDecimalPlaces(t *rapid.T, f float64) uint32 {
 	}
 }
 
+func TestIsFinite(t *testing.T) {
+	a, err := NewDecFromString("1.5")
+	require.NoError(t, err)
+
+	require.True(t, a.IsFinite())
+
+	b, err := NewDecFromString("NaN")
+	require.NoError(t, err)
+
+	require.False(t, b.IsFinite())
+}
+
 func TestReduce(t *testing.T) {
 	a, err := NewDecFromString("1.30000")
 	require.NoError(t, err)