public void TestProductErrorsChanged()
{
const decimal validValue = 5M;
const decimal invalidValue = -5M;
// Create a product with valid data
var product = new Product(Guid.NewGuid(), "Test", validValue);
// Check that no errors are reported
Assert.IsFalse(product.HasErrors);
Assert.IsTrue(string.IsNullOrEmpty(
product.GetErrors(null).Cast<string>().First()));
// Change product to invalid content and validate if
// events are properly raised
product.CheckIf(p => p.CostsPerItem = invalidValue)
.Raised(nameof(Product.CostsPerItem))
.RaisedErrorsChanged(nameof(Product.CostsPerItem));
// Check if error status is reported
Assert.IsTrue(product.HasErrors);
Assert.IsFalse(string.IsNullOrEmpty(
product.GetErrors(null).Cast<string>().First()));
Assert.IsFalse(string.IsNullOrEmpty(
product.GetErrors(nameof(Product.CostsPerItem)).Cast<string>().First()));
Assert.IsTrue(string.IsNullOrEmpty(
product.GetErrors(nameof(Product.Description)).Cast<string>().First()));
// Call setter with identical value and check that events
// are not raised
product.CheckIf(p => p.CostsPerItem = p.CostsPerItem)
.DidNotRaise(nameof(Product.CostsPerItem))
.DidNotRaiseErrorsChanged(nameof(Product.CostsPerItem));
// Call setter with valid value and check that events
// are properly raised.
product.CheckIf(p => p.CostsPerItem = validValue)
.Raised(nameof(Product.CostsPerItem))
.RaisedErrorsChanged(nameof(Product.CostsPerItem));
// Check error status has been set to OK
Assert.IsFalse(product.HasErrors);
Assert.IsTrue(string.IsNullOrEmpty(
product.GetErrors(null).Cast<string>().First()));
}