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GerstITS.Examples.Tests/Customers/Validation/CustomerValidationRuleTest.cs

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+using AwesomeAssertions;
+using GerstITS.Examples.Logic.Customers;
+using GerstITS.Examples.Logic.Customers.Validation;
+using GerstITS.TestFramework;
+using Xunit;
+
+namespace GerstITS.Examples.Tests.Customers.Validation;
+
+[TestCategory(TestCategories.Unit)]
+public sealed class CustomerValidationRuleTest
+{
+    #region Tests
+
+    [Fact]
+    public void If_a_customer_is_complete___It_is_valid()
+    {
+        var customer = CreateCustomer();
+
+        var result = new CustomerValidationRule().Validate((object)customer);
+
+        result.IsValid.Should().BeTrue();
+    }
+
+    [Fact]
+    public void If_the_first_name_is_missing___It_is_invalid()
+    {
+        var customer = CreateCustomer();
+        customer.FirstName = string.Empty;
+
+        var result = new CustomerValidationRule().Validate((object)customer);
+
+        result.IsValid.Should().BeFalse();
+    }
+
+    [Fact]
+    public void If_the_email_has_no_valid_format___It_is_invalid()
+    {
+        var customer = CreateCustomer();
+        customer.EMail = "not-an-email";
+
+        var result = new CustomerValidationRule().Validate((object)customer);
+
+        result.IsValid.Should().BeFalse();
+    }
+
+    [Fact]
+    public void If_a_customer_type_is_checked___It_can_be_validated()
+    {
+        new CustomerValidationRule().CanValidate(typeof(Customer)).Should().BeTrue();
+    }
+
+    #endregion
+
+    #region Methods
+
+    private static Customer CreateCustomer()
+    {
+        return new Customer
+               {
+                   FirstName = "Erika",
+                   LastName = "Mustermann",
+                   EMail = "erika.mustermann@example.com"
+               };
+    }
+
+    #endregion
+}