diff --git a/test.lua b/test.lua
new file mode 100644
index 0000000..a8f30bb
--- /dev/null
+++ b/test.lua
@@ -0,0 +1,32 @@
+local tests = require("test_util")
+local dbg = require("debugger")
+
+local function do_nothing() end
+
+local function func1()
+	dbg()
+end
+
+local function func2()
+	func1()
+	local _ = nil -- padding
+end
+
+local function func3()
+	func2()
+	do_nothing()
+end
+
+tests.run_test(tests.step, function()
+	func3()
+end)
+
+tests.run_test(tests.next, function()
+	func3()
+end)
+
+tests.run_test(tests.finish, function()
+	func3()
+end)
+
+print("TESTS COMPLETE")
diff --git a/test_util.lua b/test_util.lua
new file mode 100644
index 0000000..ce6e101
--- /dev/null
+++ b/test_util.lua
@@ -0,0 +1,91 @@
+-- Hack to disable color support
+local getenv = os.getenv
+os.getenv = function(sym) return (sym == "TERM") and "dumb" or getenv(sym) end
+
+local dbg = require("debugger");
+local dbg_read = dbg.read
+local dbg_write = dbg.write
+
+function string.strip(str) return str:match("^%s*(.-)%s*$") end
+
+local module = {}
+
+-- Debugger command line string to run next.
+local command_string
+local function cmd(str) command_string = str end
+
+dbg.read = function()
+	local str = command_string
+	-- command_string = nil
+	return str
+end
+
+local function sanity_write(str)
+	print "ERROR: dbg.write caled unexpectedly?!"
+	print(str)
+end
+
+local function expect(str)
+	local str2 = coroutine.yield():strip()
+	if str ~= str2 then
+		print("FAILURE")
+		print("expected: "..str)
+		print("got     : "..str2)
+	end
+end
+
+-- Used for setting up new tests.
+local function show()
+	print("expect \""..coroutine.yield():strip().."\"")
+end
+
+local function skip()
+	coroutine.yield()
+end
+
+function module.run_test(test, test_body)
+	local coro = coroutine.create(test)
+	coroutine.resume(coro)
+	
+	dbg.write = function(str) coroutine.resume(coro, str) end
+	test_body()
+	dbg.write = sanity_write
+	
+	if coroutine.status(coro) ~= "dead" then
+		print("FAILURE: test coroutine not complete")
+	end
+end
+
+function module.step()
+	cmd "s"; expect "test.lua:8 in 'func1'"
+	cmd "s"; expect "test.lua:12 in 'func2'"
+	cmd "s"; expect "test.lua:13 in 'func2'"
+	cmd "s"; expect "test.lua:17 in 'func3'"
+	cmd "s"; expect "test.lua:4 in 'do_nothing'"
+	cmd "s"; expect "test.lua:18 in 'func3'"
+	cmd "s"; expect "test.lua:22 in 'test_body'"
+	print("STEP TESTS COMPLETE")
+	cmd "c"
+end
+
+function module.next()
+	cmd "n"; expect "test.lua:8 in 'func1'"
+	cmd "n"; expect "test.lua:12 in 'func2'"
+	cmd "n"; expect "test.lua:13 in 'func2'"
+	cmd "n"; expect "test.lua:17 in 'func3'"
+	cmd "n"; expect "test.lua:18 in 'func3'"
+	cmd "n"; expect "test.lua:26 in 'test_body'"
+	print("NEXT TESTS COMPLETE")
+	cmd "c"
+end
+
+function module.finish()
+	cmd "f"; expect "test.lua:8 in 'func1'"
+	cmd "f"; expect "test.lua:12 in 'func2'"
+	cmd "f"; expect "test.lua:17 in 'func3'"
+	cmd "f"; expect "test.lua:30 in 'test_body'"
+	print("FINISH TESTS COMPLETE")
+	cmd "c"
+end
+
+return module