tests: move to t, allow yath test from root

By moving the tests subdirectory to t, we gain the ability to run `yath
test` with no arguments from inside `nix develop` in the root of the
the repo.

(`nix develop` is necessary in order to set the proper env vars for
`yath` to find our test libraries.)

t/jobs/git-update.sh

@@ -0,0 +1,56 @@
+#! /bin/sh
+# This script is used both by git & deepgit checks.
+set -e
+
+repo=git-repo
+export HOME=$(pwd)
+export XDG_CONFIG_HOME=$(pwd)/.config
+STATE_FILE=$(pwd)/.git-state
+if test -e $STATE_FILE; then
+    state=$(cat $STATE_FILE)
+    test $state -gt 3 && state=0
+else
+    state=0;
+fi
+
+echo "STATE: $state"
+case $state in
+    (0) echo "::Create repo. -- continue -- updated::"
+    git init $repo
+    cd $repo
+    git config --global user.email "you@example.com"
+    git config --global user.name "Your Name"
+
+    touch foo
+    git add foo
+    git commit -m "Add foo"
+    git tag -a -m "First Tag." tag0
+    ;;
+    (1) echo "::Create new commit. -- continue -- updated::"
+    cd $repo
+    # Increase depth to make sure the tag is not fetched by default.
+    echo 0 > foo
+    git add foo
+    git commit -m "Increase depth 0"
+    echo 1 > foo
+    git add foo
+    git commit -m "Increase depth 1"
+    echo 2 > foo
+    git add foo
+    git commit -m "Increase depth 2"
+    echo 0 > bar
+    git add bar
+    git commit -m "Add bar with 0"
+    ;;
+    (2) echo "::Amend commit. (push -f) -- continue -- updated::"
+    cd $repo
+    echo 1 > bar
+    git add bar
+    git commit --amend -m "Add bar with 1"
+    ;;
+    (*) echo "::End. -- stop -- nothing::"
+    rm -rf $repo
+    ;;
+esac
+
+echo $(($state + 1)) > $STATE_FILE