@Test
  public void testAllocateFileSuccess() throws Exception {
    String filePath = tempDir.getAbsolutePath() + File.separator + "13_0_log";
    File file = new File(filePath);
    // Validate if pool has enough files
    assertFalse(file.exists());
    assertEquals(SEGMENT_COUNT, getReservePoolRemainingSegmentCount(STORE_ID, SEGMENT_CAPACITY));
    // Call allocateFile
    fileStore.allocateFile(filePath, STORE_ID);
    // Validate if file is created
    assertTrue(file.exists());
    assertEquals(SEGMENT_COUNT-1, getReservePoolRemainingSegmentCount(STORE_ID, SEGMENT_CAPACITY));
  }
Tests the successful allocation of a file using the allocateFile method.
Verifies that:
- The file is created successfully.
- The reserve pool count is updated correctly.
ambry-store/src/test/java/com/github/ambry/store/FileStoreTest.java