feat: add plugins for zsh

.zsh/zsh-you-should-use/tests/test_buffer.zunit

@@ -0,0 +1,53 @@
+#!/usr/bin/env zunit
+
+@setup {
+    load "../you-should-use.plugin.zsh"
+    unset YSU_MESSAGE_POSITION
+    _YSU_BUFFER=""
+}
+
+@teardown {
+    rm -f output.txt
+}
+
+# We work around not being able to use `run` AND test variable values by redirecting
+# all output to a temporary file from which we can read.
+
+@test 'ysu - _write_ysu_buffer before' {
+    YSU_MESSAGE_POSITION="before"
+    export _YSU_BUFFER
+
+    _write_ysu_buffer "hello world" 2> output.txt
+
+    assert $state equals 0
+
+    assert "$(< output.txt)" same_as "hello world"
+    assert "$_YSU_BUFFER" is_empty
+}
+
+@test 'ysu - _write_ysu_buffer after' {
+    YSU_MESSAGE_POSITION="after"
+    export _YSU_BUFFER
+
+    _write_ysu_buffer "hello world" 2> output.txt
+
+    assert $state equals 0
+
+    assert "$(< output.txt)" is_empty
+    assert "$_YSU_BUFFER" same_as "hello world"
+}
+
+@test 'ysu - _write_ysu_buffer invalid' {
+    YSU_MESSAGE_POSITION="invalid"
+    export _YSU_BUFFER
+
+    _write_ysu_buffer "" 2> output.txt
+
+    assert $state equals 0
+
+    expected="$(tput setaf 1)$(tput bold)Unknown value for YSU_MESSAGE_POSITION 'invalid'. "
+    expected+="Expected value 'before' or 'after'$(tput sgr0)\n"
+
+    assert "$(< output.txt)" same_as "$expected"
+    assert "$_YSU_BUFFER" is_empty
+}