diff --git a/test/lib/layout-helpers/__get_first_window_index.test.sh b/test/lib/layout-helpers/__get_first_window_index.test.sh
new file mode 100755
index 0000000..ef34372
--- /dev/null
+++ b/test/lib/layout-helpers/__get_first_window_index.test.sh
@@ -0,0 +1,40 @@
+#! /usr/bin/env bash
+source "../../test-helper.sh"
+source "${root}/lib/layout-helpers.sh"
+
+#
+# __get_first_window_index() tests.
+#
+
+# Setup.
+libexec="${root}/libexec"
+export TMUXIFIER_TMUX_OPTS="-L tmuxifier-tests"
+session="test"
+
+
+# When first window has a index of 0.
+tmux $TMUXIFIER_TMUX_OPTS new-session -d -s $session
+assert "__get_first_window_index" "0"
+tmux $TMUXIFIER_TMUX_OPTS kill-server
+
+# When first window has a index of 1.
+tmux $TMUXIFIER_TMUX_OPTS new-session -d -s $session
+tmux $TMUXIFIER_TMUX_OPTS new-window -t "$session:1"
+tmux $TMUXIFIER_TMUX_OPTS kill-window -t "$session:0"
+assert "__get_first_window_index" "1"
+tmux $TMUXIFIER_TMUX_OPTS kill-server
+
+# When first window has a index of 2.
+tmux $TMUXIFIER_TMUX_OPTS new-session -d -s $session
+tmux $TMUXIFIER_TMUX_OPTS new-window -t "$session:2"
+tmux $TMUXIFIER_TMUX_OPTS kill-window -t "$session:0"
+assert "__get_first_window_index" "2"
+tmux $TMUXIFIER_TMUX_OPTS kill-server
+
+
+# Tear down.
+unset TMUXIFIER_TMUX_OPTS
+unset session
+
+# End of tests.
+assert_end "__get_first_window_index()"