Extract method find_element into a generic method findElementBy(type,value)

To keep the method find_element simple and easier to use, we can extract it into a generic method findElementBy(type,value).

And we will rewrite the methods in "buy_book.rb" as following:

def searchByKeyword (keyword)
    searchKeyword=findElementBy("id","twotabsearchtextbox")
    searchKeyword.clear
    searchKeyword.send_keys keyword
    element=findElementBy("class", "nav-submit-input")
    element.click
end

def openTheFirstItemInSearchResult
    element=findElementBy("xpath", "//div[@id=\"result_0\"]//span[@class=\"lrg bold\"]")
    element.click
end
def getCurrentItemTitle
    @bookTitle=findElementBy("id", "productTitle").text
end
def addToShoppingCart
    element=findElementBy("name", "submit.add-to-cart")
    element.click
end
def verifyItemAddedToShoppingCart
    confirm=findElementBy("id", "confirm-text")
    confirm.text.include?("1 item added to Cart")
end
def verifyItemAddedShownInShoppingCart
    book=findElementBy("xpath", "//div[@class=\"a-row a-size-base word-break\"]/a")
    book.attribute("title").should == @bookTitle
end
def findElementBy (type, value)
    if type=="class"
        element=@driver.find_element :class => value
    elsif type=="css"
        element=@driver.find_element :css => value
    elsif type=="id"
        element=@driver.find_element :id => value
    elsif type=="link"
        element=@driver.find_element :link => value
    elsif type=="name"
        element=@driver.find_element :name => value
    elsif type=="partial_link"
        element=@driver.find_element :partial_link_text => value
    elsif type=="tag"
        element=@driver.find_element :tag_name => value
    elsif type=="xpath"
        element=@driver.find_element :xpath => value
    else
        p "incorrect selector type"
    end
end