public class SampleEquatable : IEquatable<SampleEquatable>
{
    private int value;

    public SampleEquatable(int value)
    {
        this.value = value;
    }

    public override int GetHashCode()
    {
        return value.GetHashCode();
    }

    public override bool Equals(object obj)
    {
        return Equals(obj as SampleEquatable);
    }

    public bool Equals(SampleEquatable other)
    {
        return !Object.ReferenceEquals(other, null) 
            && (value == other.value);
    }

    public static bool operator ==(SampleEquatable left, SampleEquatable right)
    {
        return (Object.ReferenceEquals(left, null)
            && Object.ReferenceEquals(right, null))
            || (!Object.ReferenceEquals(left, null) 
            && left.Equals(right));
    }

    public static bool operator !=(SampleEquatable left, SampleEquatable right)
    {
        return !(left == right);
    }
}

public class SampleEquatableTest
{
    [VerifyContract]
    public readonly IContract EqualityTests = new EqualityContract<SampleEquatable>
    {
        ImplementsOperatorOverloads = true, // Optional (default is true)
        EquivalenceClasses =
        {
            { new SampleEquatable(1) },
            { new SampleEquatable(2) },
            { new SampleEquatable(3) },
            { new SampleEquatable(4) },
            { new SampleEquatable(5) }
        }
    };
}