patcht3200: replace hardcoded null OID with $ZERO_OID

Taking into consideration the SHA-256 transition, the test suite must be updated to support the length of the underlying hash algorithm. Tests that rely on hardcoded 40-character strings to represent the null object ID will fail when run in a SHA-256 environment, which expects a 64-character hash.

Replace the hardcoded 40-zero string in the 'git branch --merged' test with the '$ZERO_OID' variable which is provided by the test framework. This ensures the test dynamically adapts to the correct null OID length and functions correctly regardless of the active hash algorithm.

Signed-off-by: Siddharth Shrimali <r.siddharth.shrimali@gmail.com>
---
 t/t3200-branch.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

On Wed, Mar 11, 2026 at 04:28:10PM +0530, Siddharth Shrimali wrote:

I expect that the failure reason before and after this change is different, right? And likewise, I expect that before the change, the failure with SHA1 is likely different than the one with SHA256.

Taking a peek, that's indeed the case. With SHA1 we get:

    error: option `merged' must point to a commit

But with SHA256 we get:

    fatal: malformed object name 0000000000000000000000000000000000000000

So the only reason why we didn't detect that the test is broken with SHA256 is that we didn't verify the error message. Do we maybe want to make the test a bit less fragile by using something like `test_grep "must point to a commit"` on the error message?

Patrick

To support the SHA-256 transition, replace the hardcoded 40-zero string in 'git branch --merged' with '$ZERO_OID'. The current 40-character string causes the test to fail prematurely in SHA-256 environments because Git identifies a "malformed object name" (due to the 40 vs 64 character mismatch) before it even validates the object type.

By using '$ZERO_OID', we ensure the hash length is always correct for the active algorithm. Additionally, use 'test_grep' to verify the "must point to a commit" error message, ensuring the test validates the object type logic rather than just string syntax.

Suggested-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Siddharth Shrimali <r.siddharth.shrimali@gmail.com>
---
Changes in V2:
- Updated the test to capture stderr and use 'test_grep' to verify the 
  error message. This ensures the failure is due to the object type 
  check ("must point to a commit") rather than a hash length mismatch.
- Improved the commit message to add detail to the 40 vs 64 character
  mismatch and the "premature failure" in SHA-256.

 t/t3200-branch.sh | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

On 2026-03-11 at 17:41:20, Siddharth Shrimali wrote:

Yeah, this seems reasonable. It's failing, but for the wrong reasons, so checking the error message in addition to switching to `$ZERO_OID` seems like the right thing to do.

On Wed, Mar 11, 2026 at 11:11:20PM +0530, Siddharth Shrimali wrote:

"Suggested-by" is a bit strong, as it indicates that I have suggested to work on this in the first place. "Helped-by" would have been a bit of a better fit.

No reason to reroll though, this patch looks good to me. Thanks!

Patrick