Add a few Checks (#248)

- Add some basic tests for several built-in programs.
 - Preserve the state of the shell between tests

src/test/resources/test-rom/spec/programs/edit_spec.lua

@@ -0,0 +1,11 @@
+local capture = require "test_helpers".capture_program
+
+describe("The edit program", function()
+
+    it("displays its usage when given no argument", function()
+        multishell = nil
+        
+        expect(capture(stub, "edit"))
+            :matches { ok = true, output = "Usage: edit <path>\n", error = "" }
+    end)
+end)