**Core Concept**
Dubin Johnson syndrome is a rare genetic disorder characterized by chronic jaundice due to an inability to secrete conjugated bilirubin into the bile. The underlying principle being tested is the diagnosis of this condition through a specific test.

**Why the Correct Answer is Right**
The correct test used to diagnose Dubin Johnson syndrome is not provided, however, it is known that the disorder is often diagnosed through a combination of clinical presentation, laboratory tests, and imaging studies.

**Why Each Wrong Option is Incorrect**
**Option A:** Without the specific test provided, it's challenging to determine why each option is incorrect, but typically, options might include tests that are not specific for diagnosing Dubin Johnson syndrome.
**Option B:** Similarly, without the specific details, it's hard to pinpoint why this option is incorrect, but it might involve a test that is not commonly used for this diagnosis.
**Option C:** This option might be incorrect because it could involve a test that is more relevant to other liver conditions or bilirubin-related disorders.
**Option D:** Without the specific test, it's speculative, but this option could be incorrect if it represents a test that is not typically used in the diagnostic workup for Dubin Johnson syndrome.

**Clinical Pearl / High-Yield Fact**
A key point to remember is that Dubin Johnson syndrome is a rare condition, and its diagnosis often involves ruling out other causes of jaundice and liver dysfunction.

**Correct Answer:** Correct Answer: D. Cormack test