matlus · October 5, 2023 21:02
diff --git a/ModelBuilder.cs b/ModelBuilder.cs
 using System;
 using System.Collections.Generic;
 using System.Linq.Expressions;
 using System.Reflection;

 namespace ModelBuilderInTestingExample;

 public sealed class ModelBuilder<T> where T : class
 {
    private readonly Dictionary<string, object?> _propertiesAssignedUsingSet = new Dictionary<string, object?>(StringComparer.OrdinalIgnoreCase);
    private readonly Dictionary<string, object?> _propertiesAssignedUsingFor = new Dictionary<string, object?>(StringComparer.OrdinalIgnoreCase);
    private readonly Type _type;
    private readonly ParameterInfo[]? _constructorParameterInfos;

    public ModelBuilder()
    {
        _type = typeof(T);
        var constructors = _type.GetConstructors(BindingFlags.Public | BindingFlags.Instance | BindingFlags.DeclaredOnly);

        foreach (var constructor in constructors)
        {
            var parameterInfos = constructor.GetParameters();
            if (parameterInfos.Length == 0) continue;
            _constructorParameterInfos = parameterInfos;
            break;
        }
    }

    /// <summary>
    /// At the time of constructing an instance of the Builder, you should call the For method
    /// Each time you call this method you can assign a delegate to a property of your model
    /// This delegate will be called in order to set the value of the property in question
    /// You should call the For method once for each property of your model.
    /// </summary>
    /// <typeparam name="TValue"></typeparam>
    /// <param name="propertyNameExpression"></param>
    /// <param name="valueGetterDelegate"></param>
    /// <returns></returns>
    public ModelBuilder<T> For<TValue>(Expression<Func<T, TValue>> propertyNameExpression, Func<object> valueGetterDelegate)
    {
        var memberExpression = (MemberExpression)propertyNameExpression.Body;
        var propertyName = memberExpression.Member.Name;
        _propertiesAssignedUsingFor[propertyName] = valueGetterDelegate;
        return this;
    }

    /// <summary>
    /// In your unit test methods you'll generally call the Set method for each property you want to take control of in your test.
    /// Call the Set method for each property whose value you want to change from a randomly generated value.
    /// </summary>
    /// <typeparam name="TValue"></typeparam>
    /// <param name="propertyNameExpression"></param>
    /// <param name="value"></param>
    /// <returns></returns>
    public ModelBuilder<T> Set<TValue>(Expression<Func<T, TValue>> propertyNameExpression, TValue value)
    {
        var memberExpression = (MemberExpression)propertyNameExpression.Body;
        var propertyName = memberExpression.Member.Name;
        _propertiesAssignedUsingSet[propertyName] = value;
        return this;
    }

    /// <summary>
    /// Before calling the Build Method, you may want to do the following:
    /// 1. Use the For method to assign delegates (method that will set the property) for each of the properties of your model
    /// 2. Use the Set method to override/control the random value being set for one or more properties.
    /// 3. Then call the Build Method 
    /// </summary>
    /// <returns></returns>
    public T Build()
    {
        T instance = CreateInstanceUsingSetOrDefaultProperties();
        _propertiesAssignedUsingSet.Clear();
        return instance;
    }

    private T CreateInstanceUsingSetOrDefaultProperties()
    {
        var constructorParams = new object[_constructorParameterInfos!.Length];
        for (var i = 0; i < _constructorParameterInfos.Length; i++)
        {
            var parameterInfo = _constructorParameterInfos[i];
            constructorParams[i] = GetPropertyValue(parameterInfo.Name!, parameterInfo.ParameterType.Name)!;
        }

        var instance = (T)Activator.CreateInstance(_type, constructorParams)!;
        return instance;
    }

    private object? GetPropertyValue(string propertyName, string propertyTypeName)
    {
        if (_propertiesAssignedUsingSet.TryGetValue(propertyName, out var setValue))
        {
            return setValue;
        }

        if (_propertiesAssignedUsingFor.TryGetValue(propertyName, out var forValueDelegate))
        {
            return ((Func<object>)forValueDelegate!)();
        }

        throw new ModelBuilderPropertyNotSetException($"The builder was not given a value or delegate to set the value of {_type.Name}.{propertyName} property of type {propertyTypeName}. Please use the Set or For methods on the builder to specify a value for the property.");
    }
 }
	using System;
	using System.Collections.Generic;
	using System.Linq.Expressions;
	using System.Reflection;

	namespace ModelBuilderInTestingExample;

	public sealed class ModelBuilder<T> where T : class
	{
	private readonly Dictionary<string, object?> _propertiesAssignedUsingSet = new Dictionary<string, object?>(StringComparer.OrdinalIgnoreCase);
	private readonly Dictionary<string, object?> _propertiesAssignedUsingFor = new Dictionary<string, object?>(StringComparer.OrdinalIgnoreCase);
	private readonly Type _type;
	private readonly ParameterInfo[]? _constructorParameterInfos;

	public ModelBuilder()
	{
	_type = typeof(T);
	var constructors = _type.GetConstructors(BindingFlags.Public \| BindingFlags.Instance \| BindingFlags.DeclaredOnly);

	foreach (var constructor in constructors)
	{
	var parameterInfos = constructor.GetParameters();
	if (parameterInfos.Length == 0) continue;
	_constructorParameterInfos = parameterInfos;
	break;
	}
	}

	/// <summary>
	/// At the time of constructing an instance of the Builder, you should call the For method
	/// Each time you call this method you can assign a delegate to a property of your model
	/// This delegate will be called in order to set the value of the property in question
	/// You should call the For method once for each property of your model.
	/// </summary>
	/// <typeparam name="TValue"></typeparam>
	/// <param name="propertyNameExpression"></param>
	/// <param name="valueGetterDelegate"></param>
	/// <returns></returns>
	public ModelBuilder<T> For<TValue>(Expression<Func<T, TValue>> propertyNameExpression, Func<object> valueGetterDelegate)
	{
	var memberExpression = (MemberExpression)propertyNameExpression.Body;
	var propertyName = memberExpression.Member.Name;
	_propertiesAssignedUsingFor[propertyName] = valueGetterDelegate;
	return this;
	}

	/// <summary>
	/// In your unit test methods you'll generally call the Set method for each property you want to take control of in your test.
	/// Call the Set method for each property whose value you want to change from a randomly generated value.
	/// </summary>
	/// <typeparam name="TValue"></typeparam>
	/// <param name="propertyNameExpression"></param>
	/// <param name="value"></param>
	/// <returns></returns>
	public ModelBuilder<T> Set<TValue>(Expression<Func<T, TValue>> propertyNameExpression, TValue value)
	{
	var memberExpression = (MemberExpression)propertyNameExpression.Body;
	var propertyName = memberExpression.Member.Name;
	_propertiesAssignedUsingSet[propertyName] = value;
	return this;
	}

	/// <summary>
	/// Before calling the Build Method, you may want to do the following:
	/// 1. Use the For method to assign delegates (method that will set the property) for each of the properties of your model
	/// 2. Use the Set method to override/control the random value being set for one or more properties.
	/// 3. Then call the Build Method
	/// </summary>
	/// <returns></returns>
	public T Build()
	{
	T instance = CreateInstanceUsingSetOrDefaultProperties();
	_propertiesAssignedUsingSet.Clear();
	return instance;
	}

	private T CreateInstanceUsingSetOrDefaultProperties()
	{
	var constructorParams = new object[_constructorParameterInfos!.Length];
	for (var i = 0; i < _constructorParameterInfos.Length; i++)
	{
	var parameterInfo = _constructorParameterInfos[i];
	constructorParams[i] = GetPropertyValue(parameterInfo.Name!, parameterInfo.ParameterType.Name)!;
	}

	var instance = (T)Activator.CreateInstance(_type, constructorParams)!;
	return instance;
	}

	private object? GetPropertyValue(string propertyName, string propertyTypeName)
	{
	if (_propertiesAssignedUsingSet.TryGetValue(propertyName, out var setValue))
	{
	return setValue;
	}

	if (_propertiesAssignedUsingFor.TryGetValue(propertyName, out var forValueDelegate))
	{
	return ((Func<object>)forValueDelegate!)();
	}

	throw new ModelBuilderPropertyNotSetException($"The builder was not given a value or delegate to set the value of {_type.Name}.{propertyName} property of type {propertyTypeName}. Please use the Set or For methods on the builder to specify a value for the property.");
	}
	}
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