horse: fix TenThousandths formatting

horse/skill.go

@@ -1,6 +1,10 @@
 package horse
 
-import "strconv"
+import (
+	"bytes"
+	"fmt"
+	"strconv"
+)
 
 type SkillID int32
 
@@ -9,11 +13,14 @@ type TenThousandths int32
 func (x TenThousandths) String() string {
 	b := make([]byte, 0, 12)
 	b = strconv.AppendInt(b, int64(x/1e4), 10)
-	b = append(b, '.')
-	if x < 0 {
-		x = -x
+	if x%1e4 != 0 {
+		if x < 0 {
+			x = -x
+		}
+		b = append(b, '.')
+		b = fmt.Appendf(b, "%04d", x%1e4)
+		b = bytes.TrimRight(b, "0")
 	}
-	b = strconv.AppendInt(b, int64(x%1e4), 10)
 	return string(b)
 }
 

horse/skill_test.go

@@ -32,3 +32,25 @@ func TestSkillStrings(t *testing.T) {
 		}
 	}
 }
+
+func TestTenThousandthsString(t *testing.T) {
+	t.Parallel()
+	cases := []struct {
+		val  horse.TenThousandths
+		want string
+	}{
+		{0, "0"},
+		{10000, "1"},
+		{-10000, "-1"},
+		{15000, "1.5"},
+		{-15000, "-1.5"},
+		{10001, "1.0001"},
+		{5000000, "500"},
+	}
+	for _, c := range cases {
+		got := c.val.String()
+		if got != c.want {
+			t.Errorf("%d: want %q, got %q", c.val, c.want, got)
+		}
+	}
+}