Using NUnit instead of MSTest

Tests/HelpersValidatorTest.cs

@@ -0,0 +1,26 @@
+using Elwig.Helpers;
+using System.Windows.Controls;
+
+namespace Tests {
+    [TestFixture]
+    [Apartment(ApartmentState.STA)]
+    public class HelpersValidatorTest {
+
+        private static TextBox CreateTextBox(string value, int caret = 0) {
+            return new() {
+                Text = value,
+                CaretIndex = caret,
+            };
+        }
+
+        [Test]
+        public void Test_CheckInteger_Simple() {
+            Assert.IsFalse(Validator.CheckInteger(CreateTextBox(""), true).IsValid);
+            Assert.IsTrue(Validator.CheckInteger(CreateTextBox(""), false).IsValid);
+            Assert.IsTrue(Validator.CheckInteger(CreateTextBox("123"), true).IsValid);
+            Assert.IsTrue(Validator.CheckInteger(CreateTextBox("456"), false).IsValid);
+            Assert.IsTrue(Validator.CheckInteger(CreateTextBox("1234"), false, 4).IsValid);
+            Assert.IsTrue(Validator.CheckInteger(CreateTextBox("4567"), false, 3).IsValid);
+        }
+    }
+}