Reintroduce Coin.IsValid() (#4558)

Closes #4556

.pending/improvements/sdk/4556-Added-IsValid-f

@@ -0,0 +1 @@
+#4556 Added IsValid function to Coin

types/coin.go

@@ -28,10 +28,8 @@ type Coin struct {
 // NewCoin returns a new coin with a denomination and amount. It will panic if
 // the amount is negative.
 func NewCoin(denom string, amount Int) Coin {
-	mustValidateDenom(denom)
-
-	if amount.LT(ZeroInt()) {
-		panic(fmt.Errorf("negative coin amount: %v", amount))
+	if err := validate(denom, amount); err != nil {
+		panic(err)
 	}
 
 	return Coin{
@@ -51,6 +49,28 @@ func (coin Coin) String() string {
 	return fmt.Sprintf("%v%v", coin.Amount, coin.Denom)
 }
 
+// validate returns an error if the Coin has a negative amount or if
+// the denom is invalid.
+func validate(denom string, amount Int) error {
+	if err := validateDenom(denom); err != nil {
+		return err
+	}
+
+	if amount.LT(ZeroInt()) {
+		return fmt.Errorf("negative coin amount: %v", amount)
+	}
+
+	return nil
+}
+
+// IsValid returns true if the Coin has a non-negative amount and the denom is vaild.
+func (coin Coin) IsValid() bool {
+	if err := validate(coin.Denom, coin.Amount); err != nil {
+		return false
+	}
+	return true
+}
+
 // IsZero returns if this represents no money
 func (coin Coin) IsZero() bool {
 	return coin.Amount.IsZero()

types/coin_test.go

@@ -48,6 +48,26 @@ func TestIsEqualCoin(t *testing.T) {
 	}
 }
 
+func TestCoinIsValid(t *testing.T) {
+	cases := []struct {
+		coin       Coin
+		expectPass bool
+	}{
+		{Coin{testDenom1, NewInt(-1)}, false},
+		{Coin{testDenom1, NewInt(0)}, true},
+		{Coin{testDenom1, NewInt(1)}, true},
+		{Coin{"Atom", NewInt(1)}, false},
+		{Coin{"a", NewInt(1)}, false},
+		{Coin{"a very long coin denom", NewInt(1)}, false},
+		{Coin{"atOm", NewInt(1)}, false},
+		{Coin{"     ", NewInt(1)}, false},
+	}
+
+	for i, tc := range cases {
+		require.Equal(t, tc.expectPass, tc.coin.IsValid(), "unexpected result for IsValid, tc #%d", i)
+	}
+}
+
 func TestAddCoin(t *testing.T) {
 	cases := []struct {
 		inputOne    Coin