**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. This is caused by mutations in the ABCC2 gene, affecting the function of the canalicular multispecific organic anion transporter (MRP2).

**Why the Correct Answer is Right**
The correct answer is a test that measures the ability of the liver to secrete conjugated bilirubin into the bile. In Dubin-Johnson syndrome, the liver is unable to secrete conjugated bilirubin, leading to its accumulation in the blood. The **Rotor test** (also known as the bromosulfophthalein (BSP) test) is used to diagnose Dubin-Johnson syndrome by measuring the uptake and excretion of BSP by the liver. Normally, BSP is rapidly excreted into the bile, but in patients with Dubin-Johnson syndrome, BSP is retained in the liver due to the impaired secretion of conjugated bilirubin.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it is not a specific test used to diagnose Dubin-Johnson syndrome.
* **Option B:** This option is incorrect because it is a test used to diagnose other liver disorders, not Dubin-Johnson syndrome.
* **Option D:** This option is incorrect because it is a test used to diagnose other conditions, not related to liver function.

**Clinical Pearl / High-Yield Fact**
Dubin-Johnson syndrome is a rare genetic disorder that affects the liver's ability to secrete conjugated bilirubin into the bile, leading to chronic jaundice. The Rotor test is a specific test used to diagnose this condition by measuring the uptake and excretion of BSP by the liver.

**Correct Answer:** C.