test: ensure that git-mergetool(1) works with large files

test/test-mergetool.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+
+. "test/testlib.sh"
+
+begin_test "mergetool works with large files"
+(
+  set -e
+
+  reponame="mergetool-works-with-large-files"
+  git init "$reponame"
+  cd "$reponame"
+
+  git lfs track "*.dat"
+  printf "base" > conflict.dat
+  git add .gitattributes conflict.dat
+  git commit -m "initial commit"
+
+  git checkout -b conflict
+  printf "b" > conflict.dat
+  git add conflict.dat
+  git commit -m "conflict.dat: b"
+
+  git checkout master
+
+  printf "a" > conflict.dat
+  git add conflict.dat
+  git commit -m "conflict.dat: a"
+
+  set +e
+  git merge conflict
+  set -e
+
+  git config mergetool.inspect.cmd '
+    for i in BASE LOCAL REMOTE; do
+      echo "\$$i=$(eval "cat \"\$$i\"")";
+    done;
+    exit 1
+  '
+  git config mergetool.inspect.trustExitCode true
+
+  yes | git mergetool \
+      --no-prompt \
+      --tool=inspect \
+      -- conflict.dat 2>&1 \
+    | tee mergetool.log
+
+  grep "\$BASE=base" mergetool.log
+  grep "\$LOCAL=a" mergetool.log
+  grep "\$REMOTE=b" mergetool.log
+)
+end_test