对于带有身份验证和用户上下文的gRPC单元测试，我的解决方案是以下方法：

public static ProtoBuf.Grpc.CallContext TestCallContext(Guid user)
{
    var serverCallContext = TestServerCallContext.Create(
                                            method: nameof(IGrpcGreetingService.Greeting)
                                        , host: "localhost"
                                        , deadline: DateTime.Now.AddMinutes(30)
                                        , requestHeaders: new Metadata()
                                        , cancellationToken: CancellationToken.None
                                        , peer: "10.0.0.25:5001"
                                        , authContext: null
                                        , contextPropagationToken: null
                                        , writeHeadersFunc: (metadata) => Task.CompletedTask
                                        , writeOptionsGetter: () => new WriteOptions()
                                        , writeOptionsSetter: (writeOptions) => { }
                                        );

    var claims = new[] {
            new Claim(JwtRegisteredClaimNames.Sub, "some subject"),
            new Claim(JwtRegisteredClaimNames.Iat, DateTime.UtcNow.ToString()),
            new Claim(JwtRegisteredClaimNames.Name, user.ToString())
        };
    var claimsIdentity = new ClaimsIdentity(claims);

    var httpContext = new DefaultHttpContext();
    httpContext.User = new ClaimsPrincipal(claimsIdentity);
    serverCallContext.UserState["__HttpContext"] = httpContext;

    return new ProtoBuf.Grpc.CallContext("", serverCallContext);
}

TestServerCallContext.Create的参数来自here。
也许这可以帮助别人保存一些小时或几天：）