RoverInit.cs

public sealed class Rover
{
    private readonly Terrain terrain;

    public Rover(
        Terrain terrain,
        int startingPositionX,
        int startingPositionY,
        Direction startingHeading)
    {
        if (terrain == null)
            throw new ArgumentNullException(
                nameof(terrain),
                "Rover cannot navigate on a non-existent terrain!");

        if (IsStartingPositionOutsideTerrain(
                terrain,
                startingPositionX,
                startingPositionY))
            throw new ArgumentOutOfRangeException(
                $"{nameof(startingPositionX)},{nameof(startingPositionY)}",
                "Rover cannot start outside the terrain");

        if (!Enum.IsDefined(typeof(Direction), startingHeading))
            throw new ArgumentOutOfRangeException(
                nameof(startingHeading),
                "Starting heading is invalid, must be one of NORTH, EAST, WEST or SOUTH");

        this.terrain = terrain;
        StartingPositionX = startingPositionX;
        StartingPositionY = startingPositionY;

        NewPositionX = StartingPositionX;
        NewPositionY = StartingPositionY;

        StartingHeading = startingHeading;
        NewHeading = StartingHeading;

        Id = Guid.NewGuid();
    }
}