Test Contact Validation.cs

[Test]
public void ShouldThrowExceptionIfOpenTaskExists()
{
    Entity contact = new Entity()
    {
        LogicalName = "contact",
        Id = Guid.NewGuid()
    };

    ParameterCollection parameters = new ParameterCollection();
    parameters["Target"] = contact.ToEntityReference();
    this.PipelineContextMock.Setup(p => p.InputParameters).Returns(parameters);
    this.PipelineContextMock.Setup(p => p.MessageName).Returns("Delete");
    EntityCollection tasks = new EntityCollection() { EntityName = "task", Entities = { GetRelatedTask(contact.Id) } };
    this.OrganizationServiceMock.Setup(s => s.RetrieveMultiple(It.IsAny<QueryExpression>())).Returns(tasks);

    PreValidateContactDelete plugin = new PreValidateContactDelete();
    var exception = Assert.Throws<InvalidPluginExecutionException>(() => plugin.Execute(ServiceProviderMock.Object));
    Assert.That(exception.Message, Is.StringContaining(OPEN_TASKS_EXCEPTION));
}