Erroring if no custom formatting string is specified

Author: SteveWilkes

AgileMapper.UnitTests/Configuration/WhenConfiguringStringFormatting.cs

@@ -1,6 +1,8 @@
 namespace AgileObjects.AgileMapper.UnitTests.Configuration
 {
     using System;
+    using AgileMapper.Configuration;
+    using Shouldly;
     using TestClasses;
     using Xunit;
 
@@ -51,5 +53,20 @@ public void ShouldFormatDoublesMapperWideUsingDecimalPlaces()
                 result.Value.ShouldBe("1.00");
             }
         }
+
+        [Fact]
+        public void ShouldErrorIfNoFormatSpecified()
+        {
+            var noFormatEx = Should.Throw<MappingConfigurationException>(() =>
+            {
+                using (var mapper = Mapper.CreateNew())
+                {
+                    mapper.WhenMapping
+                        .StringsFrom<double>(c => { });
+                }
+            });
+
+            noFormatEx.Message.ShouldContain("No format string specified");
+        }
     }
 }

AgileMapper/Api/Configuration/MappingConfigStartingPoint.cs

@@ -325,6 +325,8 @@ public IGlobalConfigSettings StringsFrom<TSourceValue>(Action<StringFormatSpecif
 
             formatSelector.Invoke(formatSpecifier);
 
+            formatSpecifier.ErrorIfInvalid();
+
             return this;
         }
 

AgileMapper/Configuration/StringFormatSpecifier.cs

@@ -1,6 +1,7 @@
 namespace AgileObjects.AgileMapper.Configuration
 {
     using System;
+    using ReadableExpressions.Extensions;
     using TypeConversion;
 
     /// <summary>
@@ -11,6 +12,7 @@ public class StringFormatSpecifier
     {
         private readonly MapperContext _mapperContext;
         private readonly Type _sourceType;
+        private bool _isValid;
 
         internal StringFormatSpecifier(MapperContext mapperContext, Type sourceType)
         {
@@ -26,7 +28,19 @@ internal StringFormatSpecifier(MapperContext mapperContext, Type sourceType)
         /// </param>
         public void FormatUsing(string format)
         {
+            _isValid = true;
             _mapperContext.ValueConverters.Add(new ToFormattedStringConverter(_sourceType, format));
         }
+
+        internal void ErrorIfInvalid()
+        {
+            if (_isValid)
+            {
+                return;
+            }
+
+            throw new MappingConfigurationException(
+                "No format string specified for custom string mapping from " + _sourceType.GetFriendlyName());
+        }
     }
 }