My Solution

validator.coffee

@@ -0,0 +1,69 @@
+class Validator
+    constructor: (@input, @tests) ->
+
+    validate: ->
+
+        passing = true
+        @errorMessages = []
+
+        for test in @tests
+            if not test.passes()
+                passing = false
+                @errorMessages.push test.errorMessage
+
+        return passing
+
+
+class EmailValidator extends Validator
+
+    validate: ->
+        ampersandAndPeriodTest = new Test(new RegExp("^([\\w.-]+)@([\\w.-]+)\\.([\\w.-]+)"), @input, "Invalid Email Address. Must have an ampersand and a period.")
+
+        @tests = [ampersandAndPeriodTest]
+
+        super
+
+
+class PasswordValidator extends Validator
+
+    validate: ->
+        lengthTest = new Test(new RegExp("^(.+){8,}"), @input, "Password must be at least 8 characters long.")
+        capitalTest = new Test(new RegExp(".*[A-Z]+.*"), @input, "Password must have at least one capital letter.")
+        numberTest = new Test(new RegExp(".*[0-9]+.*"), @input, "Password must have at least one number.")
+
+        @tests = [lengthTest, capitalTest, numberTest]
+
+        super
+
+
+class Test
+
+    constructor: (@regex, @input, @errorMessage) ->
+
+    passes: ->
+        @regex.test @input
+
+
+errorMessageDomElement = $("ul.errors")
+errorMessageDomElement.empty()
+
+form = $('form[name="sign_in"]')
+
+form.submit ->
+
+    errorMessageDomElement.empty()
+
+    email = form.find("input[type=text]").val()
+    password = form.find("input[type=password]").val()
+
+    emailValidator = new EmailValidator email
+    passwordValidator = new PasswordValidator password
+
+    validators = [emailValidator, passwordValidator]
+
+    validationResults = validators.map (validator) -> validator.validate()
+    errorMessages = (validators.map (validator) -> validator.errorMessages).reduce (a, b) -> a.concat b
+
+    for message in errorMessages
+        liElement = "<li>" + message  + "</li>"
+        errorMessageDomElement.append liElement