Tests: Move tests into package

Tests/Helpers/BillingTest.cs

@@ -2,9 +2,9 @@
 using Microsoft.Data.Sqlite;
 using System.Reflection;
 
-namespace Tests {
+namespace Tests.Helpers {
     [TestFixture]
-    public class HelpersBillingTest {
+    public class BillingTest {
 
         private SqliteConnection? Connection;
 

Tests/Helpers/UtilsTest.cs

@@ -1,8 +1,8 @@
 using Elwig.Helpers;
 
-namespace Tests {
+namespace Tests.Helpers {
     [TestFixture]
-    public class HelpersUtilsTest {
+    public class UtilsTest {
 
         private static readonly double[,] Gradation = new double[,] {
             { 14.0,  68.0 },

Tests/Helpers/ValidatorTest.cs

@@ -1,10 +1,10 @@
 using Elwig.Helpers;
 using System.Windows.Controls;
 
-namespace Tests {
+namespace Tests.Helpers {
     [TestFixture]
     [Apartment(ApartmentState.STA)]
-    public class HelpersValidatorTest {
+    public class ValidatorTest {
 
         private static TextBox TB(string value, int caret = 0) {
             return new() {