A sample test project file with coverlet installed

MyProject.UnitTests.csproj

<Project Sdk="Microsoft.NET.Sdk">

    <PropertyGroup>
        <TargetFramework>netcoreapp3.1</TargetFramework>

        <IsPackable>false</IsPackable>
    </PropertyGroup>

    <ItemGroup>
        <PackageReference Include="coverlet.msbuild" Version="2.9.0">
            <IncludeAssets>runtime; build; native; contentfiles; analyzers; buildtransitive</IncludeAssets>
            <PrivateAssets>all</PrivateAssets>
        </PackageReference>
        <PackageReference Include="Microsoft.EntityFrameworkCore" Version="3.1.3" />
        <PackageReference Include="Microsoft.EntityFrameworkCore.InMemory" Version="3.1.3" />
        <PackageReference Include="Microsoft.NET.Test.Sdk" Version="16.6.0" />
        <PackageReference Include="Moq" Version="4.13.1" />
        <PackageReference Include="nunit" Version="3.12.0" />
        <PackageReference Include="NUnit3TestAdapter" Version="3.16.1" />
    </ItemGroup>

    <ItemGroup>
      <ProjectReference Include="..\MyProject\MyProject.csproj" />
    </ItemGroup>

</Project>