<?xml version="1.0" encoding="utf-8" ?>

<configuration>

  <configSections>

    <<strong>section</strong> name="CustomConfigs" type="ClassLibraryNetStandard.CustomConfigHandler, ClassLibraryNetStandard"/>

  </configSections>

  <<strong>CustomConfigs</strong>>

    <CustomConfig name="service1" order="0" reflectconfig="ClassLibraryNetStandard.TestService, ClassLibraryNetStandard"/>

    <CustomConfig name="service2" order="1" reflectconfig="ClassLibraryNetStandard.TestService2, ClassLibraryNetStandard"/>

  </CustomConfigs> 

  <<strong>appSettings</strong>>

    <add key="service" value="service1"/>

  </appSettings>

</configuration>

using System;

using System.Collections.Generic;

using System.Text;

namespace ClassLibraryNetStandard

{

    public class CustomConfig

    {

        public string Name { get; set; }

        public string ReflectConfig { get; set; }

        public int Order { get; set; }

    }

}

using System;

using System.Collections.Generic;

using System.Text;

using System.Xml;

namespace ClassLibraryNetStandard

{

   public class CustomConfigHandler : System.Configuration.IConfigurationSectionHandler

    {

        public object Create(object parent, object configContext, XmlNode section)

        {

            var configs = new List<CustomConfig>();

            foreach (XmlNode childNode in section.ChildNodes)

            {

                string name = null;

                var config = new CustomConfig();

                if (childNode.Attributes["name"] != null)

                {

                    name = childNode.Attributes["name"].Value;

                    config.Name = name;

                    if (childNode.Attributes["order"] != null)

                    {

                        config.Order = Convert.ToInt32(childNode.Attributes["order"].Value);

                    }

                    if (childNode.Attributes["reflectconfig"] != null)

                    {

                        config.ReflectConfig = childNode.Attributes["reflectconfig"].Value;

                    }                 

                    configs.Add(config);

                }

            }

            return configs;

        }

    }

}

1

public static List<CustomConfig> GetCustomConfigs()

{

    var sectionConfig = System.Configuration.ConfigurationManager.GetSection("CustomConfigs");

    if (sectionConfig != null)

    {

        return  sectionConfig as List<CustomConfig>;

    }

    return null;

}

[TestMethod]

 public void ConfigTest()

 {

     var configs = ClassLibraryNetStandard.CustomConfigManager.GetCustomConfigs();

     Assert.IsNotNull(configs);

 }

1

MSTest is running as testhost.dll, which means that ConfigurationManager is reading settings from testhost.dll.config when executing under .NET core. <br>It will look for testhost.dll.config where the testhost.dll is located as the accepted answer states. <br>What is not mentioned is that it will also look for testhost.dll.config in the location where you have your test dlls.