Revision control stress tests
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Merge This!


Merge This! is a test suite for revision control tools designed to stress test their merge algorithms. Think of it as an Acid3 test for version control systems.

All version control systems have a notion of merging two separate development branches. One measure of a VCS's quality is how well it handles merges. Is it able to merge two branches without manual conflict resolution? Does the code still behave correctly after automatic resolution? If a conflict does require manual resolution, how complicated is the conflict?

Merge This! has a number of small test cases representing typical development patterns which might cause merge conflicts. Each VCS performs the merge and we evaluate the results. The goal is to codify many software revision patterns in this fashion.

Each test case contains one small C program. The branches modify this program in different ways. For a test to pass all of the following must work:

  • VCS automatically merges the two branches (no manual intervention)
  • the C program compiles
  • the compiled C program produces correct output

Failing earlier in this list is better. The worst possible scenario is a VCS that silently resolves a merge but does it in a way that breaks your program at runtime (I hope you have a good test suite :-)

Running the Tests

The tests support these tools: bzr, darcs, git, hg. To test a tool, run the appropriate make target:

$ make git

Current Results

The table of results below is based on these VCS versions:

  • Bazaar - 2.6.0
  • Darcs - 2.10.0
  • Git - 2.5.1
  • Mercurial - 3.5
  • Subversion - 1.9.5

The tests are sorted by an approximation of how hard they should be to pass.

Bazaar Darcs Git Mercurial Subversion
nearby-changes OK OK OK OK OK
same-change OK OK OK OK OK
move-modify OK OK OK OK Fail
adjacent-changes Fail OK Fail Fail OK
trailing-whitespace Fail Fail OK Fail OK
indent-block Fail Fail OK Fail OK
indent-block-py Fail Fail Fail Fail Fail
eol-comment Fail Fail Fail Fail Fail
dual-renames Fail OK Fail Fail Fail