Install-Package NUnit -Version 4.4.0
dotnet add package NUnit --version 4.4.0
<PackageReference Include="NUnit" Version="4.4.0" />
For projects that support PackageReference, copy this XML node into the project file to reference the package. 
paket add NUnit --version 4.4.0
The NuGet Team does not provide support for this client. Please contact its maintainers for support.