added another test for usage generation

README.md

@@ -8,7 +8,7 @@ Not everything stated here is implemented.
 
 Features: 
 
-* Declarative and usual interfaces. 
+* Declarative and classic interfaces. 
 
     Declarative: 
 
@@ -21,7 +21,7 @@ Features:
        :count "*"
     ```
 
-    Usual: 
+    Classic: 
 
     ```lua
     parser:argument("input", {
@@ -66,3 +66,18 @@ Features:
 * Supports default values and automatic conversions for arguments. 
 * Automatically generates error, usage  and help(__NYI__) messages. 
 * Supports commands(e.g. in [git](http://git-scm.com/) CLI `add`, `commit`, `push`, etc. are commands). Each command has its own set of options and arguments. 
+* Automatically generates tips on typos(__NYI__). 
+
+    Example: 
+
+    ```lua
+    parser:option "-f" "--from"
+    parser:command "install"
+
+    parser:parse{"--form", "there"}
+    -- Error: unknown option --form
+    -- Did you mean --from?
+
+    parser:parse{"isntall"}
+    -- Error: unknown command isntall
+    -- Did you mean install?

spec/usage_spec.lua

@@ -48,6 +48,20 @@ describe("tests related to usage message generation", function()
       )
    end)
 
+   it("creates correct usage message for subcommands", function()
+      local parser = argparse.parser "foo"
+      parser:flag "-q" "--quiet"
+      local run = parser:command "run"
+      run:option "--where"
+
+      parser:prepare()
+
+      assert.equal(
+         [=[Usage: foo run [--where <where>]]=],
+         run:prepare():get_usage()
+      )
+   end)
+
    describe("usage generation can be customized", function()
       it("uses message provided by user", function()
          local parser = argparse.parser "foo"