Refactor message service and move tests to Application.Tests

Renamed IMessageService to IMessageCommandService and updated all usages accordingly. Moved and renamed test files from Govor.API.Tests to the new Govor.Application.Tests project, updating namespaces to match. Refactored message-related services and controllers to use the new naming and structure. Added Govor.Application.Tests project to the solution.

Govor.Application.Tests/Validators/UsernameValidatorTests.cs

@@ -0,0 +1,43 @@
+using Govor.Application.Exceptions.AuthService;
+using Govor.Application.Infrastructure.Validators;
+
+namespace Govor.API.Tests.UnitTests.Services.Validators;
+
+[TestFixture]
+public class UsernameValidatorTests
+{
+    private UsernameValidator _validator;
+
+    [SetUp]
+    public void SetUp()
+    {
+        _validator = new UsernameValidator();
+    }
+
+    [TestCase("Иван")]
+    [TestCase("Алексей")]
+    [TestCase("Ёжик")]
+    [TestCase("Иван123")] // содержит цифры
+    public void Validate_ValidUsernames_ShouldNotThrow(string username)
+    {
+        Assert.DoesNotThrow(() => _validator.Validate(username));
+    }
+
+    [TestCase("Ivan")] // не кириллица
+    [TestCase("123Иван")] // начинается не с буквы
+    [TestCase("!@#$")] // спецсимволы
+    [TestCase("")] // пусто
+    [TestCase("И")] // меньше минимума
+    [TestCase("ИванИванИванИванИванИванИванИванИванИванИванИванИван")] // больше максимума (44 символа)
+    public void Validate_InvalidUsernames_ShouldThrow(string username)
+    {
+        Assert.Throws<InvalidUsernameException>(() => _validator.Validate(username));
+    }
+
+    [TestCase("Иван", ExpectedResult = true)]
+    [TestCase("1234", ExpectedResult = false)]
+    public bool TryValidate_ShouldReturnTrueRegardlessOfInput(string username)
+    {
+        return _validator.TryValidate(username);
+    }
+}