feat: add bats tests, docs (#139)

* fix(test): ensure bats file list uses xargs

* docs(readme): use yarn for testing instructions

* fix(test): ensure pipelines fail properly

* docs(alias): fix table header

---------

Signed-off-by: Ismo Vuorinen <ismo@ivuorinen.net>

tests/x-mkd.bats

@@ -0,0 +1,8 @@
+#!/usr/bin/env bats
+
+@test "x-mkd creates directory" {
+  dir="$BATS_TMPDIR/mkd-test"
+  run env VERBOSE=1 bash local/bin/x-mkd "$dir"
+  [ "$status" -eq 0 ]
+  [ -d "$dir" ]
+}