Allow a stub to return a specific value

spec/stub_spec.lua

@@ -92,4 +92,10 @@ describe("Tests dealing with stubs", function()
      assert.is_nil(s)
   end)
 
+  it("returns a given return value", function()
+    stub(test, "key", "foo")
+
+    assert.is.equal("foo", test.key())
+  end)
+
 end)

src/stub.lua

@@ -2,10 +2,9 @@
 local assert = require 'luassert.assert'
 local spy = require 'luassert.spy'
 local util = require 'luassert.util'
-local stubfunc = function() end
 local stub = {}
 
-function stub.new(object, key)
+function stub.new(object, key, return_value)
   if object == nil and key == nil then
     -- called without arguments, create a 'blank' stub
     object = {}
@@ -14,6 +13,9 @@ function stub.new(object, key)
   assert(type(object) == "table" and key ~= nil, "stub.new(): Can only create stub on a table key, call with 2 params; table, key")
   assert(object[key] == nil or util.callable(object[key]), "stub.new(): The element for which to create a stub must either be callable, or be nil")
   local old_elem = object[key]    -- keep existing element (might be nil!)
+  local stubfunc = function()
+    return return_value
+  end
   object[key] = stubfunc          -- set the stubfunction
   local s = spy.on(object, key)   -- create a spy on top of the stub function
   local spy_revert = s.revert     -- keep created revert function