fix:Property set expression builder does not accept null values and lambdas (#239)

Author: ivo-stoilov

Telerik.JustMock/Expr.cs

@@ -1,6 +1,6 @@
 /*
  JustMock Lite
- Copyright © 2022 Progress Software Corporation
+ Copyright © 2022,2025 Progress Software Corporation
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
@@ -24,15 +24,43 @@ namespace Telerik.JustMock
 {
 #if !PORTABLE
     /// <summary>
-    /// Defines helper methods used for easily building expressions.
+    /// Provides utility methods for simplifying the creation of expression trees used in mocking scenarios.
+    /// This class offers a fluent API for building property access expressions that can be used to configure
+    /// mock behavior for property getters and setters.
     /// </summary>
     public static class Expr
     {
         /// <summary>
-        /// Creates a <see cref="IPropertyExpressionBuilder<T>"/> from an expression.
-        /// Commonly used to easily build an expression for a property set.
+        /// Creates an <see cref="IPropertyExpressionBuilder{T}"/> for the specified property access expression.
+        /// This method analyzes a lambda expression that accesses a property and builds a property expression
+        /// that can be used to configure mock behavior for property getters or setters.
         /// </summary>
-        /// <typeparam name="T">The type of the property.</typeparam>
+        /// <typeparam name="T">The type of the property being accessed.</typeparam>
+        /// <param name="expression">
+        /// A lambda expression representing the property access, such as <c>() => obj.Property</c> for
+        /// instance properties or <c>() => Class.StaticProperty</c> for static properties.
+        /// </param>
+        /// <returns>
+        /// An <see cref="IPropertyExpressionBuilder{T}"/> that provides fluent methods for configuring
+        /// property getter and setter behavior in mock objects.
+        /// </returns>
+        /// <exception cref="ArgumentException">
+        /// Thrown when the provided expression is not a property access expression. The expression must
+        /// be in the form of accessing a property, such as <c>obj.Property</c> or <c>Class.StaticProperty</c>.
+        /// </exception>
+        /// <exception cref="MockException">
+        /// Thrown when attempting to mock a field instead of a property. JustMock only supports mocking
+        /// properties, not fields.
+        /// </exception>
+        /// <example>
+        /// <code>
+        /// // Setting up a mock for a property getter
+        /// Mock.Arrange(Expr.Property(() => mock.SomeProperty)).Returns(expectedValue);
+        /// 
+        /// // Setting up a mock for a property setter
+        /// Mock.Arrange(Expr.Property(() => mock.SomeProperty).Set(Arg.IsAny&lt;string&gt;).DoNothing();
+        /// </code>
+        /// </example>
         public static IPropertyExpressionBuilder<T> Property<T>(Expression<Func<T>> expression)
         {
             return ProfilerInterceptor.GuardInternal(() =>
@@ -41,8 +69,7 @@ public static IPropertyExpressionBuilder<T> Property<T>(Expression<Func<T>> expr
 
                 if (memberExpression.NodeType != ExpressionType.MemberAccess)
                 {
-                    throw new MockException("Wrong expression used, property access expression looks like obj.Property or Class.StaticProperty");
-
+                    throw new ArgumentException("Wrong expression used, property access expression looks like obj.Property or Class.StaticProperty", nameof(expression));
                 }
 
                 MemberExpression outerMemberExpression = (MemberExpression)memberExpression;

Telerik.JustMock/IPropertyExpressionBuilder.cs

@@ -1,6 +1,6 @@
 /*
  JustMock Lite
- Copyright © 2022 Progress Software Corporation
+ Copyright © 2022,2025 Progress Software Corporation
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
@@ -22,19 +22,39 @@ namespace Telerik.JustMock
 {
 #if !PORTABLE
     /// <summary>
-    /// Defines methods for setting and getting property values through an expression.
+    /// Defines methods for building LINQ expressions that represent property get and set operations.
+    /// This interface is used to facilitate setting up expectations and verifications for property
+    /// access. It provides a strongly-typed approach to creating expressions that can be used
+    /// to intercept, verify, and emulate property behavior during testing.
     /// </summary>
     public interface IPropertyExpressionBuilder<T>
     {
         /// <summary>
-        /// Builds and expresison for setting the vlaue of a property.
+        /// Builds an expression for property set arrangement with a specific value.
+        /// This method creates an expression that represents assigning the specified value to the property,
+        /// which can be used to verify that a property was set to a particular value or to arrange
+        /// behavior when such an assignment occurs.
         /// </summary>
-        /// <typeparam name="value">The value that should be set to the property.</typeparam>
+        /// <param name="value">The exact value to match when the property is set.</param>
+        /// <returns>An Action expression representing the property set operation.</returns>
         Expression<Action> Set(T value);
 
         /// <summary>
-        /// Builds and expresison for getting the vlaue of a property.
+        /// Builds an expression for property set arrangement using a lambda.
+        /// This method allows for more complex matching logic when arranging property set operations,
+        /// such as matching ranges of values or applying custom validation criteria.
         /// </summary>
+        /// <param name="expression">A lambda expression that produces the value to match when the property is set.</param>
+        /// <returns>An Action expression representing the property set operation with the specified matching logic.</returns>
+        Expression<Action> Set(Expression<Func<T>> expression);
+
+        /// <summary>
+        /// Builds an expression for property get arrangement.
+        /// This method creates an expression that represents retrieving the value of the property,
+        /// which can be used to arrange behavior when the property is accessed, such as returning
+        /// specific values or throwing exceptions.
+        /// </summary>
+        /// <returns>A Func expression representing the property get operation.</returns>
         Expression<Func<T>> Get();
     }
 #endif

Telerik.JustMock/Mock.Arrange.cs

@@ -1,6 +1,6 @@
 /*
  JustMock Lite
- Copyright © 2010-2015,2018 Progress Software Corporation
+ Copyright © 2010-2015,2018,2025 Progress Software Corporation
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
@@ -158,13 +158,14 @@ public static ActionExpectation ArrangeSet(Action action)
                 if (Mock.IsOnDemandEnabled)
                 {
                     var sb = new StringBuilder();
-                    sb.AppendLine("ArrangeSet(Action) is not avaiable with OnDemand option enabled.");
-                    sb.AppendLine("Please use Mock.ArrangeSet<OwnerTypeOfProperty>(Action). Or Mock.Arrange with appropriate expression for property set.");
-                    sb.AppendLine("-------------");
-                    sb.AppendLine("Example 1:");
-                    sb.AppendLine("Mock.ArrangeSet<TypeOfMockObject>(() => mockObject.SomeProperty = 5);");
-                    sb.AppendLine("Example 2:");
-                    sb.AppendLine("Mock.Arrange(Expr.Property(() => mockObject.SomeProperty).Set(5));");
+                    sb.AppendLine("ArrangeSet(Action) is not compatible with the OnDemand feature.");
+                    sb.AppendLine("Please use one of these alternatives:");
+                    sb.AppendLine("  1. Mock.ArrangeSet<OwnerTypeOfProperty>(Action)");
+                    sb.AppendLine("  2. Mock.Arrange(Expression) with a property set expression");
+                    sb.AppendLine();
+                    sb.AppendLine("Examples:");
+                    sb.AppendLine("  Mock.ArrangeSet<MockObject>(() => mockObject.SomeProperty = 5);");
+                    sb.AppendLine("  Mock.Arrange(Expr.Property(() => mockObject.SomeProperty).Set(5));");
 
                     throw new MockException(sb.ToString());
                 }

Telerik.JustMock/PropertyExpressionBuilder.cs

@@ -1,6 +1,6 @@
 /*
  JustMock Lite
- Copyright © 2022 Progress Software Corporation
+ Copyright © 2022,2025 Progress Software Corporation
 
    Licensed under the Apache License, Version 2.0 (the "License");
    you may not use this file except in compliance with the License.
@@ -34,22 +34,24 @@ public PropertyExpressionBuilder(Expression propertyExpression)
             this.propertyExpression = propertyExpression;
         }
 
-        /// <summary>
-        /// Builds and expresison for setting the vlaue of a property.
-        /// </summary>
-        /// <typeparam name="value">The value that should be set to the property.</typeparam>
         public Expression<Action> Set(T value)
         {
             return ProfilerInterceptor.GuardInternal(() =>
             {
                 return Expression.Lambda<Action>(
-                    Expression.Assign(this.propertyExpression, Expression.Constant(value)));
+                    Expression.Assign(this.propertyExpression, Expression.Constant(value, typeof(T))));
+            });
+        }
+
+        public Expression<Action> Set(Expression<Func<T>> expression)
+        {
+            return ProfilerInterceptor.GuardInternal(() =>
+            {
+                return Expression.Lambda<Action>(
+                    Expression.Assign(this.propertyExpression, expression.Body));
             });
         }
 
-        /// <summary>
-        /// Builds and expresison for getting the vlaue of a property.
-        /// </summary>
         public Expression<Func<T>> Get()
         {
             return ProfilerInterceptor.GuardInternal(() =>