fix: computeTrend division by zero, add tests for trend and currency parsing, add username to settings

internal/bot/rpg_test.go

@@ -1,6 +1,7 @@
 package bot
 
 import (
+	"strings"
 	"testing"
 )
 
@@ -170,4 +171,57 @@ func TestSanitizeDisplayName(t *testing.T) {
 	if got := SanitizeDisplayName("Ali\x00ce"); got != "Alice" {
 		t.Errorf("SanitizeDisplayName control: got %q", got)
 	}
+	if got := SanitizeDisplayName(""); got != "" {
+		t.Errorf("SanitizeDisplayName empty: got %q", got)
+	}
+}
+
+func TestParseCurrencyInput(t *testing.T) {
+	cases := []struct {
+		input string
+		want  string
+		ok    bool
+	}{
+		{"$ USD", "$ USD", true},
+		{"T Toman", "T Toman", true},
+		{"IRR Rial", "IRR Rial", true},
+		{"€ EUR", "€ EUR", true},
+		{"", "", false},
+		{"$", "", false},
+		{"   ", "", false},
+		{"$$$ TooLongCode", "", false},
+	}
+	for _, c := range cases {
+		got, errMsg := parseCurrencyInput(c.input)
+		if c.ok && (got != c.want || errMsg != "") {
+			t.Errorf("parseCurrencyInput(%q) = (%q, %q), want (%q, \"\")", c.input, got, errMsg, c.want)
+		}
+		if !c.ok && errMsg == "" {
+			t.Errorf("parseCurrencyInput(%q) = (%q, \"\"), want error", c.input, got)
+		}
+	}
+}
+
+func TestComputeTrendFromAvgs(t *testing.T) {
+	cases := []struct {
+		recent, older float64
+		wantPts       int
+		wantDirSub    string
+	}{
+		{0, 0, 5, "stable"},
+		{100, 0, 15, "new"},
+		{0, 100, 0, "-100"},
+		{121, 100, 15, "+21"},
+		{100, 100, 5, "stable"},
+		{100, 130, 0, "-23"},
+	}
+	for _, c := range cases {
+		pts, dir := computeTrendFromAvgs(c.recent, c.older)
+		if pts != c.wantPts {
+			t.Errorf("computeTrendFromAvgs(%.0f, %.0f) pts = %d, want %d", c.recent, c.older, pts, c.wantPts)
+		}
+		if !strings.Contains(dir, c.wantDirSub) {
+			t.Errorf("computeTrendFromAvgs(%.0f, %.0f) dir = %q, want containing %q", c.recent, c.older, dir, c.wantDirSub)
+		}
+	}
 }