Datatypes that implement a single method can be more simply
represented as ordinary functions, e.g.
(defn real-provider ...)
(defn fake-provider ...)
(defn load-page [provider ...]
(let [foo (provider)]
...))
That being said, you have other options: In clojure.test you can using
`binding` to stub out functions within your tests. Lazytest <http://
github.com/stuartsierra/lazytest> has explicit support for stubbing
out functions during testing.
-S
On Oct 11, 6:06 pm, "Felix H. Dahlke" <f...@ubercode.de> wrote:
> Hi,
>
> I'm new to Clojure, using it for a reasonably sized project for the
> first time, and I'm trying to do test-driven development.
>
> While it does work well technically - clojure.test is very nice to use
> and feels a lot like JUnit 4's assertThat() - I'm wondering if I'm
> trying to program Java in Clojure.
>
> Here's an example:
>
> I'm writing a class (Um. I mean, a ... namespace? Well, a horde of
> functions.) that accesses web pages from a backend, which can e.g. take
> these from the filesystem or from a database. In Java or C++, I'd use an
> interface for that and create one implementation for the filesystem and
> one for the database:
>
> interface Provider {
> String loadPage(String name);
>
> }
>
> This is possible in Clojure:
>
> (defprotocol Provider
> (load-page [this name])
>
> It can be implemented using deftype:
>
> (deftype DatabaseProvider []
> Provider
> (load-page [this name]
> (have-fun-with-the-database)))
>
> And I can call it like this:
>
> (load-page (DatabaseProvider.) "foo")
>
> Feels a little weird (especially since all examples of defprotocol and
> deftype use camel case for type names), but works.
>
> Back to my question: Am I trying to do Java in Clojure? Is there a more
> Lisp-y way to do this?
>
> As you may have suspected, this design wasn't my initial intention, it
> was driven by TDD: This allows me to create a mock implementation
> against which I can write my test cases without having having to depend
> on external resources. Typical TDD design. In fact, there will only be
> one backend for now.
>
> This made me wonder if test-driven development was desirable in Clojure
> at all, or even in functional programming in general.
>
> There's a few articles on the issue. Many seem to be from Clojure
> newcomers, asking questions themselves, and none handles design issues
> like mock objects [1].
>
> One guy basically said that he stopped doing TDD because the REPL makes
> it possible to test specific functions directly [2]. I can see how he
> says that the *driven* aspect of TDD can be performed by the REPL, but I
> find it too inconvenient for extensive use.
>
> Bob Martin says that, because functional programming differs from
> object-oriented programming (In my opinion, these paradigms are
> compatible - did he mean imperative programming?), test-driven
> development has to start by testing the details, and work up to testing
> the big picture. TDD in e.g. Java starts with the big picture and moves
> down. I don't understand his points completely, but if he's right, this
> might be a fundamental problem for TDD in functional languages.
>
> One guy partly disagrees with him on some matters, but doesn't really
> mention the bottom-up thing [4].
>
> What are your thoughts on these issues? Is anybody here doing TDD in
> Clojure? Is anybody against it?
>
> [1]:http://www.magpiebrain.com/2010/02/16/struggling-with-test-driven-clo...
> [2]:http://s-expressions.com/2009/07/28/clojure-the-repl-and-test-driven-...
> [3]:http://blog.objectmentor.com/articles/2010/06/03/tdd-in-clojure
> [4]:http://ericlefevre.net/wordpress/2010/06/04/bob-martin-on-tdd-in-cloj...
>
> signature.asc
> < 1KViewDownload
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