Added test to check what happens when your lambda isn't a property

Author: robdmoore

NTestDataBuilder.Tests/Entities/Customer.cs

@@ -16,6 +16,13 @@ public Customer(string firstName, string lastName, int yearJoined)
             YearJoined = yearJoined;
         }
 
+        public int CustomerForHowManyYears(DateTime since)
+        {
+            if (since.Year < YearJoined)
+                throw new ArgumentException("Date must be on year or after year that customer joined.", "since");
+            return since.Year - YearJoined;
+        }
+
         public string FirstName { get; private set; }
         public string LastName { get; private set; }
         public int YearJoined { get; private set; }

NTestDataBuilder.Tests/GetSetTests.cs

@@ -66,5 +66,14 @@ public void GivenNoValueHasBeenSetForAProperty_WhenRetrievingTheValueForThatProp
             Assert.That(ex.Message, Is.StringStarting("No value has been recorded yet for FirstName; consider using Has(x => x.FirstName) to check for a value first."));
             Assert.That(ex.ParamName, Is.EqualTo("property"));
         }
+
+        [Test]
+        public void WhenRetrievingValueForANonProperty_ThenThrowAnException()
+        {
+            var ex = Assert.Throws<ArgumentException>(() => _b.Get(x => x.CustomerForHowManyYears(DateTime.Now)));
+
+            Assert.That(ex.Message, Is.StringStarting("Given property expression (x => x.CustomerForHowManyYears(DateTime.Now)) didn't specify a property on Customer"));
+            Assert.That(ex.ParamName, Is.EqualTo("property"));
+        }
     }
 }

NTestDataBuilder/DataBuilder.cs

@@ -94,7 +94,14 @@ private static string GetPropertyName<TValue>(Expression<Func<TEntity, TValue>>
         {
             var memExp = property.Body as MemberExpression;
             if (memExp == null)
-                throw new ArgumentException("Property must be valid on the entity object", "property");
+                throw new ArgumentException(
+                    string.Format(
+                        "Given property expression ({0}) didn't specify a property on {1}",
+                        property,
+                        typeof(TEntity).Name
+                    ),
+                    "property"
+                );
 
             return memExp.Member.Name;
         }