.NET Core 3.1 - Dependency resolution failed for component - AWS Mock Lambda Test Tools

Could you try and experiment for me and in your csproj file add the property CopyLocalLockFileAssemblies with a value of true and see if that changes your behavior?

Here is a full csproj file example.

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <TargetFramework>netcoreapp3.1</TargetFramework>
    <GenerateRuntimeConfigurationFiles>true</GenerateRuntimeConfigurationFiles>
    <AWSProjectType>Lambda</AWSProjectType>
    <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Amazon.Lambda.Core" Version="1.1.0" />
    <PackageReference Include="Amazon.Lambda.Serialization.SystemTextJson" Version="1.0.0" />
    <PackageReference Include="System.Data.SqlClient" Version="4.8.1" />
  </ItemGroup>
</Project>

I had the same issue when I was trying to deploy my AWS lambda function to the AWS using Terraform.

Adding this property to my lambda functions .csproj file fixed the issue -

<PropertyGroup>
  <CopyLocalLockFileAssemblies>true</CopyLocalLockFileAssemblies>
</PropertyGroup>