NOTE: Test on In-Portal with `Custom` module installed.
1. add these lines to `/modules/custom/install/project_upgrades.sql` file (empty line on top !)
```
lang=sql
# r2: Revision 2
SELECT UNIX_TIMESTAMP();
# r3: Revision 3
SELECT UNIX_TIMESTAMP();
```
2. login to admin console as root
3. go to {nav Tools > System Tools} section
4. press `Deploy` button
5. confirm you see message, that contains:
```
Upgrading Database ...
# r1: Initial Project Task (#TASK_ID)
# r2: Revision 2
SELECT UNIX_TIMESTAMP() ... OK (1)
# r3: Revision 3
SELECT UNIX_TIMESTAMP() ... OK (1)
```
6. add these lines to `/modules/custom/install/project_upgrades.sql` file (empty line on top !)
```
lang=sql
# r2: Revision 2 (duplicated)
SELECT UNIX_TIMESTAMP();
```
7. press `Deploy` button again
8. confirm you see message
```
Verifying Database Revisions ... FAILED
Duplicate revision #2 found
```
9. replace these lines in `/modules/custom/install/project_upgrades.sql` file (empty line on top !)
```
lang=sql
# r2: Revision 2 (duplicated)
SELECT UNIX_TIMESTAMP();
```
by (empty line on top !)
```
lang=sql
# r4: Revision 4
SELECT UNIX_TIMESTAMP();
# r4: Revision 4 (duplicated)
SELECT UNIX_TIMESTAMP();
```
10. press `Deploy` button again
11. confirm you see message
```
Verifying Database Revisions ... FAILED
Duplicate revision #4 found
```