lua: add a simple test for both vis.pipe variants

test/lua/pipe.in

@@ -0,0 +1 @@
+foo

test/lua/pipe.lua

@@ -0,0 +1,24 @@
+require 'busted.runner'()
+
+local file = vis.win.file
+
+describe("vis.pipe", function()
+
+	it("vis.pipe buffer", function()
+		vis:pipe("foo", "cat > f")
+		local f = io.open("f", "r")
+		assert.truthy(f)
+		assert.are.equal(f:read("*a"), "foo")
+		f:close()
+		os.remove("f")
+	end)
+
+	it("vis.pipe range", function()
+		vis:pipe(file, {start=0, finish=3}, "cat > f")
+		local f = io.open("f", "r")
+		assert.truthy(f)
+		assert.are.equal(f:read("*a"), "foo")
+		f:close()
+		os.remove("f")
+	end)
+end)