How about this test table ?
CREATE TABLE [dbo].[Test] (
[TestId] INT IDENTITY (1, 1) NOT NULL,
[ExamId] INT NULL,
[ObjectiveId] INT NULL,
[CustomId] INT NULL,
[Title] NVARCHAR (100) NULL,
[Status] INT NOT NULL
FOREIGN KEY (ExamId) REFERENCES [dbo].[Exam](ExamId)
FOREIGN KEY (ObjectiveId) REFERENCES [dbo].[Objective](ObjectiveId)
FOREIGN KEY (CustomId) REFERENCES [dbo].[Custom](CustomId)
);