如何使用JRuby和Mocha模拟静态Java方法？

Question

My goal is to unit test legacy Java code, riddled with static utility methods, using JRuby and Mocha. Is this possible?

I am trying to apply similar techniques that are available in JMockit; a framework leveraging proxies to change test behavior dynamically. Purists may suggest refactoring out the static methods, but at this point, it's just not possible.

I put together two unit tests:

Test #1 - Ruby Mocking - my control.
Test #2 - Java Mocking - to see if I can accomplish the same in Java.

For both tests, I'm replacing the "getTax" method.

Here is the code:

Test 1

require 'rubygems'
require 'dust'
require 'mocha'

unit_tests do

    # Test 1 - Stub out JRuby secondary class and override the "getTax" method
    # This is my "control" - I'm overriding the tax multiplier from 1.15 to 1.18.
    # It works =)
    test "RubyMocking" do
        # System Under Test
        class RInvoice 
            def initialize
                @util = RInvoiceUtil.new
            end
            def calculate
                @util.getTax * 10.0
            end
        end

        # Dependency
        class RInvoiceUtil 
            # we'll stub out this method and change the tax rate
            def getTax
                1.15
            end
        end

        invoice = RInvoice.new      
        # change the tax rate
        RInvoiceUtil.any_instance.stubs(:getTax).returns(1.18)      
        assert_equal(invoice.calculate.to_s, "11.8")
    end
end

Test 2

include Java

require 'rubygems'
require 'dust'
require 'mocha'
require 'invoice.jar'
Invoice = Java::example.Invoice
InvoiceUtil = Java::example.InvoiceUtil

unit_tests do

# Test 2 - Stub out Java class InvoiceUtil and it's *static* getTax method.
# This can be achieved via JMockit, but is it possible in Mocha?

  test "JavaMocking" do
    invoice = Invoice.new       
    # this does not work because the ruby objects are only 
    # proxies to the java objects?
    InvoiceUtil.any_instance.stubs(:getTax).returns(1.18)       
    assert_equal(invoice.calculate, 11.8)   
  end
end

Test 2 fails with: <11.5> expected but was <11.8> . Ok, so I can't do that. Hmm. Is the reason this does not work because the ruby objects are only proxies to the java objects?

Java Source

package example;
public class Invoice {
    public double calculate() {
        return InvoiceUtil.getTax() * 10.0;
    }
}

public class InvoiceUtil {
    public static double getTax() {
        return 1.15;
    }
}

To Sum Up

All I want to do is combine static method mocking with JRuby to leverage (1) easy scripting with (2) flexibile test isolation.

Thanks in advance for your responses!

Answer 1

I realize this question was asked a long time ago, but I came along a very similar problem and finally got it working. I think the problem is in your usage of any_instance...

At least in my scenario the solution was to call stubs directly on the class containing the static method:

InvoiceUtil.stubs(:getTax).returns(1.18)

Answer 2

I haven't used this myself, but Ola Bini released JtestR a while ago which might be what you're looking for. It looks like he has addressed the any_instance problem you are seeing above. I have no idea how up-to-date JtestR is, but looking at Ola's GitHub account there are some recent commits , so you could be in luck. I hope this helps.