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-rev-update.sh

@@ -0,0 +1,31 @@
+#! /bin/sh
+set -e
+
+repo=git-repo
+export HOME=$(pwd)
+export XDG_CONFIG_HOME=$(pwd)/.config
+STATE_FILE=$(pwd)/.git-rev-state
+if test -e $STATE_FILE; then
+    state=1
+    rm $STATE_FILE
+else
+    state=0
+    touch $STATE_FILE
+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_AUTHOR_DATE="1970-01-01T00:00:00 +0000" GIT_COMMITTER_DATE="1970-01-01T00:00:00 +0000" git commit -m "Add foo"
+    ;;
+    (*) echo "::End. -- stop -- nothing::"
+    rm -rf $repo
+    ;;
+esac