[test] check unique colors for themes via test

This avoids the check to be run on every instantiation.
It also revealed that the old check did not work properly and revealed
two duplicates in the ugly theme.

test/theme.go

@@ -39,13 +39,13 @@ func NewTheme() fyne.Theme {
 			theme.ColorNameHeaderBackground:  red(22),
 			theme.ColorNameInputBackground:   red(30),
 			theme.ColorNameInputBorder:       gray(10),
-			theme.ColorNameMenuBackground:    red(30),
+			theme.ColorNameMenuBackground:    red(50),
 			theme.ColorNameOnPrimary:         red(200),
 			theme.ColorNameOverlayBackground: red(44),
 			theme.ColorNamePlaceHolder:       blue(200),
 			theme.ColorNamePressed:           blue(250),
 			theme.ColorNamePrimary:           green(255),
-			theme.ColorNameScrollBar:         blue(200),
+			theme.ColorNameScrollBar:         blue(220),
 			theme.ColorNameSeparator:         gray(30),
 			theme.ColorNameSelection:         red(55),
 			theme.ColorNameShadow:            blue(150),
@@ -136,14 +136,6 @@ func Theme() fyne.Theme {
 }
 
 func newConfigurableTheme(name string, colors map[fyne.ThemeColorName]color.Color, fonts map[fyne.TextStyle]fyne.Resource, sizes map[fyne.ThemeSizeName]float32) fyne.Theme {
-	seen := map[color.Color]fyne.ThemeColorName{}
-	for cn, c := range colors {
-		if seen[c] != "" {
-			// This panic will never happen on released code because it will happen on CI runs prior release.
-			panic(fmt.Sprintf("duplicate color value %#v for color %s already used for color %s in theme %s", c, cn, seen[c], name))
-		}
-		seen[c] = cn
-	}
 	return &configurableTheme{
 		colors: colors,
 		fonts:  fonts,

test/theme_test.go

@@ -0,0 +1,32 @@
+package test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+
+	"fyne.io/fyne/v2"
+)
+
+func Test_NewTheme_checkForUniqueColors(t *testing.T) {
+	th := NewTheme().(*configurableTheme)
+	seen := map[string]fyne.ThemeColorName{}
+	for cn, c := range th.colors {
+		r, g, b, a := c.RGBA()
+		key := fmt.Sprintf("%d %d %d %d", r, g, b, a)
+		assert.True(t, seen[key] == "", "color value %#v for color %s already used for color %s in theme %s", c, cn, seen[key], th.name)
+		seen[key] = cn
+	}
+}
+
+func Test_Theme_checkForUniqueColors(t *testing.T) {
+	th := Theme().(*configurableTheme)
+	seen := map[string]fyne.ThemeColorName{}
+	for cn, c := range th.colors {
+		r, g, b, a := c.RGBA()
+		key := fmt.Sprintf("%d %d %d %d", r, g, b, a)
+		assert.True(t, seen[key] == "", "color value %#v for color %s already used for color %s in theme %s", c, cn, seen[key], th.name)
+		seen[key] = cn
+	}
+}