test-reach: create new test tool for ref_newer

As we prepare to change the behavior of the algorithms in
commit-reach.c, create a new test-tool subcommand 'reach' to test these
methods on interesting commit-graph shapes.

To use the new test-tool, use 'test-tool reach <method>' and provide
input to stdin that describes the inputs to the method. Currently, we
only implement the ref_newer method, which requires two commits. Use
lines "A:<committish>" and "B:<committish>" for the two inputs. We will
expand this input later to accommodate methods that take lists of
commits.

The test t6600-test-reach.sh creates a repo whose commits form a
two-dimensional grid. This grid makes it easy for us to determine
reachability because commit-A-B can reach commit-X-Y if and only if A is
at least X and B is at least Y. This helps create interesting test cases
for each result of the methods in commit-reach.c.

We test all methods in three different states of the commit-graph file:
Non-existent (no generation numbers), fully computed, and mixed (some
commits have generation numbers and others do not).

Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 1 insertions, 0 deletions

diff --git a/Makefile b/Makefile
index 59781f4..d69f9d4 100644
--- a/Makefile
+++ b/Makefile
@@ -716,6 +716,7 @@ TEST_BUILTINS_OBJS += test-mktemp.o
 TEST_BUILTINS_OBJS += test-online-cpus.o
 TEST_BUILTINS_OBJS += test-path-utils.o
 TEST_BUILTINS_OBJS += test-prio-queue.o
+TEST_BUILTINS_OBJS += test-reach.o
 TEST_BUILTINS_OBJS += test-read-cache.o
 TEST_BUILTINS_OBJS += test-ref-store.o
 TEST_BUILTINS_OBJS += test-regex.o