extract limit computing logic into a func and add a test

Author: rusq

auth/auth_ui/huh.go

@@ -33,8 +33,8 @@ import (
 )
 
 const (
-	defQRCodeSz = 9000 // default limit for encoded image size, seen values 6174, 8462
-	maxQRCodeSz = 1<<16 - 1
+	defQRCodeSz = 9000      // default limit for encoded image size, seen values 6174, 8462
+	maxQRCodeSz = 1<<16 - 1 // maximum allowed QR code image size.
 	imgPrefix   = "data:image/png;base64,"
 )
 
@@ -267,15 +267,10 @@ func (*Huh) RequestQR(ctx context.Context, _ io.Writer) (string, error) {
   3. right-click the QR code image;
   4. choose Copy Image.`
 
-	// check limQrCodeSz value for sanity
-	if limQrCodeSz < defQrCodeSz || maxQrCodeSz < limQrCodeSz {
-		limQrCodeSz = defQrCodeSz
-	}
-
 	var imageData string
 	q := huh.NewForm(huh.NewGroup(
 		huh.NewText().
-			CharLimit(limQrCodeSz).
+			CharLimit(qrCharLimit()).
 			Value(&imageData).
 			Validate(func(s string) error {
 				if !strings.HasPrefix(s, imgPrefix) {
@@ -292,3 +287,12 @@ func (*Huh) RequestQR(ctx context.Context, _ io.Writer) (string, error) {
 	}
 	return imageData, nil
 }
+
+// qrCharLimit returns the effective character limit for the QR code input
+// field.
+func qrCharLimit() int {
+	if defQRCodeSz <= limQRCodeSz && limQRCodeSz <= maxQRCodeSz {
+		return limQRCodeSz
+	}
+	return defQRCodeSz
+}

auth/auth_ui/huh_test.go

@@ -15,7 +15,9 @@
 
 package auth_ui
 
-import "testing"
+import (
+	"testing"
+)
 
 func Test_valSixDigits(t *testing.T) {
 	type args struct {
@@ -60,3 +62,27 @@ func Test_valSixDigits(t *testing.T) {
 		})
 	}
 }
+
+func Test_qrCharLimit(t *testing.T) {
+	tests := []struct {
+		name    string
+		limQRsz int
+		want    int
+	}{
+		{"zero", 0, defQRCodeSz},
+		{"default", defQRCodeSz, defQRCodeSz},
+		{"between allowed values", (maxQRCodeSz - defQRCodeSz) / 2, (maxQRCodeSz - defQRCodeSz) / 2},
+		{"over maximum", maxQRCodeSz + 1, defQRCodeSz},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			var old = limQRCodeSz
+			limQRCodeSz = tt.limQRsz
+			t.Cleanup(func() { limQRCodeSz = old })
+
+			if got := qrCharLimit(); got != tt.want {
+				t.Errorf("qrCharLimit() = %v, want %v", got, tt.want)
+			}
+		})
+	}
+}