add string test for coin and coins (cosmos#6547)

Co-authored-by: Alexander Bezobchuk <alexanderbez@users.noreply.github.com>

go.mod

@@ -39,7 +39,6 @@ require (
 	github.com/tendermint/iavl v0.14.0-rc1
 	github.com/tendermint/tendermint v0.33.5
 	github.com/tendermint/tm-db v0.5.1
-	golang.org/x/sync v0.0.0-20190911185100-cd5d95a43a6e
 	google.golang.org/grpc v1.30.0
 	gopkg.in/yaml.v2 v2.3.0
 )

types/coin_test.go

@@ -1,6 +1,7 @@
 package types
 
 import (
+	"fmt"
 	"strings"
 	"testing"
 
@@ -27,6 +28,11 @@ func TestCoin(t *testing.T) {
 	require.Equal(t, NewInt(5), NewCoin(testDenom1, NewInt(5)).Amount)
 }
 
+func TestCoin_String(t *testing.T) {
+	coin := NewCoin(testDenom1, NewInt(10))
+	require.Equal(t, fmt.Sprintf("10%s", testDenom1), coin.String())
+}
+
 func TestIsEqualCoin(t *testing.T) {
 	cases := []struct {
 		inputOne Coin
@@ -188,6 +194,43 @@ func TestCoinIsZero(t *testing.T) {
 // ----------------------------------------------------------------------------
 // Coins tests
 
+func TestCoins_String(t *testing.T) {
+	cases := []struct {
+		name     string
+		input    Coins
+		expected string
+	}{
+		{
+			name:     "empty coins",
+			input:    Coins{},
+			expected: "",
+		},
+		{
+			name: "single coin",
+			input: Coins{
+				{"tree", NewInt(1)},
+			},
+			expected: "1tree",
+		},
+		{
+			name: "multiple coins",
+			input: Coins{
+				{"tree", NewInt(1)},
+				{"gas", NewInt(1)},
+				{"mineral", NewInt(1)},
+			},
+			expected: "1tree,1gas,1mineral",
+		},
+	}
+
+	for _, tt := range cases {
+		tt := tt
+		t.Run(tt.name, func(t *testing.T) {
+			require.Equal(t, tt.expected, tt.input.String())
+		})
+	}
+}
+
 func TestIsZeroCoins(t *testing.T) {
 	cases := []struct {
 		inputOne Coins