Add some error formatting tests

Thanks to them i discovered that the parser errors where indicating the wrong token ¬¬

src/coffee-script.coffee

@@ -141,5 +141,9 @@ parser.yy.parseError = (message, {loc, token}) ->
   # Disregard Jison's message, it contains redundant line numer information.
   message = "unexpected #{token}"
 
+  # FIXME The `loc` received does not correspond to the `token` token, but to
+  # the one before it instead. That's why the test in error_messages.coffee is
+  # failing. There should be a way to get the location data... maybe accessing
+  # the lexer's tokens?
   {first_line, first_column, last_line, last_column} = loc
   throw new CompilerError message, first_line, first_column, last_line, last_column

test/error_messages.coffee

@@ -0,0 +1,42 @@
+# Error Formating
+# ---------------
+
+# Ensure that errors of different kinds (lexer, parser and compiler) are shown
+# in a consistent way.
+
+assertErrorFormat = (code, expectedErrorFormat) ->
+  throws (-> CoffeeScript.compile code), (err) ->
+    eq expectedErrorFormat, (err.prettyMessage 'test.coffee', code)
+    yes
+
+test "lexer errors formating", ->
+  assertErrorFormat '''
+    normalObject    = {}
+    insideOutObject = }{
+  ''',
+  '''
+    test.coffee:2:19: error: unmatched }
+    insideOutObject = }{
+                      ^
+  '''
+
+# FIXME Test not passing. See "parser.yy.parseError" in coffee-script.coffee
+test "parser error formating", ->
+  assertErrorFormat '''
+    foo in bar or in baz
+  ''',
+  '''
+    test.coffee:1:12: error: unexpected RELATION
+    foo in bar or in baz
+                  ^^
+  '''
+
+test "compiler error formatting", ->
+  assertErrorFormat '''
+    evil = (foo, eval, bar) ->
+  ''',
+  '''
+    test.coffee:1:14: error: parameter name "eval" is not allowed
+    evil = (foo, eval, bar) ->
+                 ^^^^
+  '''