Merge PR cosmos#4303: Fix coins findDup()

.pending/bugfixes/sdk/4303-Fix-NewCoins-un

@@ -0,0 +1 @@
+#4303 Fix NewCoins() underlying function for duplicate coins detection.

types/coin.go

@@ -646,11 +646,12 @@ func findDup(coins Coins) int {
 		return -1
 	}
 
-	prevDenom := coins[0]
+	prevDenom := coins[0].Denom
 	for i := 1; i < len(coins); i++ {
-		if coins[i] == prevDenom {
+		if coins[i].Denom == prevDenom {
 			return i
 		}
+		prevDenom = coins[i].Denom
 	}
 
 	return -1

types/coin_test.go

@@ -593,3 +593,31 @@ func TestCoinsIsAnyGT(t *testing.T) {
 	require.False(t, Coins{twoBtc, twoAtom, threeEth}.IsAnyGT(Coins{fiveAtom, sixEth}))
 	require.False(t, Coins{twoAtom, sixEth}.IsAnyGT(Coins{twoBtc, fiveAtom}))
 }
+
+func TestFindDup(t *testing.T) {
+	abc := NewInt64Coin("abc", 10)
+	def := NewInt64Coin("def", 10)
+	ghi := NewInt64Coin("ghi", 10)
+
+	type args struct {
+		coins Coins
+	}
+	tests := []struct {
+		name string
+		args args
+		want int
+	}{
+		{"empty", args{NewCoins()}, -1},
+		{"one coin", args{NewCoins(NewInt64Coin("xyz", 10))}, -1},
+		{"no dups", args{Coins{abc, def, ghi}}, -1},
+		{"dup at first position", args{Coins{abc, abc, def}}, 1},
+		{"dup after first position", args{Coins{abc, def, def}}, 2},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			if got := findDup(tt.args.coins); got != tt.want {
+				t.Errorf("findDup() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}