A simple test infrastructure -- idea stolen from Gaurav.

src/platform/vboot_reference/cgptlib/cgpt.h

 /* Copyright (c) 2010 The Chromium OS Authors. All rights reserved.
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef VBOOT_REFERENCE_CGPT_H_
 #define VBOOT_REFERENCE_CGPT_H_
 
 #include <stdint.h>
 
 enum {
-        GPT_ERROR_INVALID_HEADERS = 1,
-        GPT_ERROR_INVALID_ENTRIES,
-        GPT_ERROR_INVALID_SECTOR_SIZE,
-        GPT_ERROR_INVALID_SECTOR_NUMBER,
+  GPT_ERROR_NO_VALID_KERNEL = 1,
+  GPT_ERROR_INVALID_HEADERS,
+  GPT_ERROR_INVALID_ENTRIES,
+  GPT_ERROR_INVALID_SECTOR_SIZE,
+  GPT_ERROR_INVALID_SECTOR_NUMBER,
 };
 
 #define GPT_MODIFIED_HEADER1 0x01
 #define GPT_MODIFIED_HEADER2 0x02
 #define GPT_MODIFIED_ENTRIES1 0x04
 #define GPT_MODIFIED_ENTRIES2 0x08
 
 #define GPT_UPDATE_ENTRY_TRY 1
   /* System will be trying to boot the currently selected kernel partition.
    * Update its try count if necessary. */
 #define GPT_UPDATE_ENTRY_BAD 2
   /* The currently selected kernel partition failed validation.  Mark entry as
    * invalid. */
 
 struct GPTData {
-        /* Fill in the following fields before calling GPTInit() */
-        uint8_t *header1;       /* GPT primary header, from sector 1 of disk
-                                 *   (size: 512 bytes) */
-        uint8_t *header2;       /* GPT secondary header, from last sector of
-                                 *   disk (size: 512 bytes) */
-        uint8_t *entries1;      /* primary GPT table, follows primary header
-                                 *   (size: 16 KB) */
-        uint8_t *entries2;      /* secondary GPT table, precedes secondary
-                                 *   header (size: 16 KB) */
-        uint32_t sector_bytes;  /* Size of a LBA sector, in bytes */
-        uint64_t drive_sectors; /* Size of drive in LBA sectors, in sectors */
+  /* Fill in the following fields before calling GPTInit() */
+  uint8_t *header1;       /* GPT primary header, from sector 1 of disk
+                           *   (size: 512 bytes) */
+  uint8_t *header2;       /* GPT secondary header, from last sector of
+                           *   disk (size: 512 bytes) */
+  uint8_t *entries1;      /* primary GPT table, follows primary header
+                           *   (size: 16 KB) */
+  uint8_t *entries2;      /* secondary GPT table, precedes secondary
+                           *   header (size: 16 KB) */
+  uint32_t sector_bytes;  /* Size of a LBA sector, in bytes */
+  uint64_t drive_sectors; /* Size of drive in LBA sectors, in sectors */
 
-        /* Outputs */
-        uint8_t modified;       /* Which inputs have been modified?
-                                 * 0x01 = header1
-                                 * 0x02 = header2
-                                 * 0x04 = table1
-                                 * 0x08 = table2  */
+  /* Outputs */
+  uint8_t modified;       /* Which inputs have been modified?
+                           * 0x01 = header1
+                           * 0x02 = header2
+                           * 0x04 = table1
+                           * 0x08 = table2  */
 
-        /* Internal state */
-        uint8_t current_kernel; // the current kernel index
+  /* Internal state */
+  uint8_t current_kernel; // the current kernel index
 };
 typedef struct GPTData GPTData_t;
 
 int GPTInit(GPTData_t *gpt);
 /* Initializes the GPT data structure's internal state.  The header1, header2,
  * table1, table2, and drive_size fields should be filled in first.
  *
  * On return the modified field may be set, if the GPT data has been modified
  * and should be written to disk.
  *
  * Returns 0 if successful, non-zero if error:
  *   GPT_ERROR_INVALID_HEADERS, both partition table headers are invalid, enters
  *                              recovery mode,
  *   GPT_ERROR_INVALID_ENTRIES, both partition table entries are invalid, enters
  *                              recovery mode,
  *   GPT_ERROR_INVALID_SECTOR_SIZE, size of a sector is not supported,
  *   GPT_ERROR_INVALID_SECTOR_NUMBER, number of sectors in drive is invalid (too
  *                                    small) */
 
 int GPTNextKernelEntry(GPTData_t *gpt, uint64_t *start_sector, uint64_t *size);
 /* Provides the location of the next kernel partition, in order of decreasing
  * priority.  On return the start_sector parameter contains the LBA sector
  * for the start of the kernel partition, and the size parameter contains the
  * size of the kernel partition in LBA sectors.
  *
- * Returns 0 if successful, 1 if error or no more sectors.  */
+ * Returns 0 if successful, else
+ *   GPT_ERROR_NO_VALID_KERNEL, no avaliable kernel, enters recovery mode */
 
 int GPTUpdateKernelEntry(GPTData_t *gpt, uint32_t update_type);
 /* Updates the kernel entry with the specified index, using the specified type
  * of update (GPT_UPDATE_ENTRY_*).
  *
  * On return the modified field may be set, if the GPT data has been modified
  * and should be written to disk.
  *
  * Returns 0 if successful, 1 if error. */
 
-#endif  // VBOOT_REFERENCE_CGPT_H_
+#endif  /* VBOOT_REFERENCE_CGPT_H_ */