I have used SOAP in Ruby when i've had to make a fake SOAP server for my acceptance tests. I don't know if this was the best way to approach the problem, but it worked for me. 
I have used Sinatra gem (I wrote about creating mocking endpoints with Sinatra here) for server and also Nokogiri for XML stuff (SOAP is working with XML).
So, for the beginning I have create two files (e.g. config.rb and responses.rb) in which I have put the predefined answers that SOAP server will return. 
In config.rb I have put the WSDL file, but as a string. 
@@wsdl = '<wsdl:definitions name="StockQuote"
         targetNamespace="http://example.com/stockquote.wsdl"
         xmlns:tns="http://example.com/stockquote.wsdl"
         xmlns:xsd1="http://example.com/stockquote.xsd"
         xmlns:soap="http://schemas.xmlsoap.org/wsdl/soap/"
         xmlns="http://schemas.xmlsoap.org/wsdl/">
         .......
      </wsdl:definitions>'
In responses.rb I have put samples for responses that SOAP server will return for different scenarios.
@@login_failure = "<s:Envelope xmlns:s="http://schemas.xmlsoap.org/soap/envelope/">
    <s:Body>
        <LoginResponse xmlns="http://tempuri.org/">
            <LoginResult xmlns:a="http://schemas.datacontract.org/2004/07/WEBMethodsObjects" xmlns:i="http://www.w3.org/2001/XMLSchema-instance">
                <a:Error>Invalid username and password</a:Error>
                <a:ObjectInformation i:nil="true"/>
                <a:Response>false</a:Response>
            </LoginResult>
        </LoginResponse>
    </s:Body>
</s:Envelope>"
So now let me show you how I have actually created the server.
require 'sinatra'
require 'json'
require 'nokogiri'
require_relative 'config/config.rb'
require_relative 'config/responses.rb'
after do
# cors
headers({
    "Access-Control-Allow-Origin" => "*",
    "Access-Control-Allow-Methods" => "POST",
    "Access-Control-Allow-Headers" => "content-type",
})
# json
content_type :json
end
#when accessing the /HaWebMethods route the server will return either the WSDL file, either and XSD (I don't know exactly how to explain this but it is a WSDL dependency)
get "/HAWebMethods/" do
  case request.query_string
    when 'xsd=xsd0'
        status 200
        body = @@xsd0
    when 'wsdl'
        status 200
        body = @@wsdl
  end
end
post '/HAWebMethods/soap' do
request_payload = request.body.read
request_payload = Nokogiri::XML request_payload
request_payload.remove_namespaces!
if request_payload.css('Body').text != ''
    if request_payload.css('Login').text != ''
        if request_payload.css('email').text == some username && request_payload.css('password').text == some password
            status 200
            body = @@login_success
        else
            status 200
            body = @@login_failure
        end
    end
end
end
I hope you'll find this helpful!