**Core Concept**
The diagnosis of a vesicovaginal fistula (VVF) involves assessing the communication between the bladder and vagina, which leads to urinary incontinence. A definitive diagnosis requires identifying this abnormal connection.

**Why the Correct Answer is Right**
The most important test for diagnosing VVF is the **Fistula Grading Test** or the **Fistula Cystogram**, which involves filling the bladder with a contrast agent and then taking X-rays to visualize the fistula. This test helps determine the size and location of the fistula, guiding further management.

**Why Each Wrong Option is Incorrect**
**Option A:** The **Voiding Cystourethrogram (VCUG)** is used to diagnose urethral or bladder neck abnormalities, but it may not be as effective in identifying a VVF.

**Option B:** The **Urinary Tract Infection (UTI) workup** may be performed to rule out other causes of dysuria, but it is not a diagnostic test for VVF.

**Option C:** The **Vaginal examination** can provide clues about the presence of a fistula, but it is not a definitive diagnostic test.

**Clinical Pearl / High-Yield Fact**
A VVF is often associated with prolonged obstructed labor, which can cause bladder and vaginal tissue necrosis, leading to fistula formation. Prompt recognition and treatment are essential to prevent long-term urinary incontinence and potential complications.

**Correct Answer: C. Vaginal examination**