Is assignment in a conditional clause good ruby style?

In order to write more concisely, rather than do this:

test_value = method_call_that_might_return_nil()if test_value  do_something_with test_valueend

I've been assigning in the conditional:

if test_value = method_call_that_might_return_nil()  do_something_with test_valueend

Is this bad style? The still-more-concise syntax:

do_something_with test_value if test_value = method_call_that_might_return_nil()

is not allowed, as discussed in another SO question, and will remain that way in 1.9, according to Matz (http://redmine.ruby-lang.org/issues/show/1141).

Given the possible confusion of assignment and comparison, does this make it too hard to read the code?