{Make an onion}

Refactoring techniques to turn your Clojure code into an onion

WORK IN PROGRESS

Separate calculations from side-effects

 (defn update-customer-email [customer-id new-email]
  (let [customer (-> (db/load-customer customer-id)      ;; I/O
                     (assoc :email (str/trim new-email))];; calculation
      (db/save-customer customer)))                      ;; I/O (defn update-customer-email [customer-id new-email]
  (let [customer (-> (db/load-customer customer-id)      ;; I/O
                     (assoc :email (str/trim new-email))];; calculation
      (db/save-customer customer)))                      ;; I/O (defn update-customer-email [customer-id new-email]
  (let [customer (-> (db/load-customer customer-id)      ;; I/O
                     (assoc :email (str/trim new-email))];; calculation
      (db/save-customer customer)))                      ;; I/O (defn update-customer-email [customer-id new-email]
  (let [customer (-> (db/load-customer customer-id)      ;; I/O
                     (assoc :email (str/trim new-email))];; calculation
      (db/save-customer customer)))                      ;; I/O

# PRESENTING CODE

How to test this?

 (deftest test-update-customer-email []
  (with-redefs [db/load-customer (constantly {:name "Han Solo" :email "han@solo.net"})
                db/save-customer #(is (= "han.solo@rebels.net" (:email %1))]
              (update-customer-email "id" "han.solo@rebels.net"))))
             (deftest test-update-customer-email []
  (with-redefs [db/load-customer (constantly {:name "Han Solo" :email "han@solo.net"})
                db/save-customer #(is (= "han.solo@rebels.net" (:email %1))]
              (update-customer-email "id" "han.solo@rebels.net"))))
             (deftest test-update-customer-email []
  (with-redefs [db/load-customer (constantly {:name "Han Solo" :email "han@solo.net"})
                db/save-customer #(is (= "han.solo@rebels.net" (:email %1))]
              (update-customer-email "id" "han.solo@rebels.net"))))
             (deftest test-update-customer-email []
  (with-redefs [db/load-customer (constantly {:name "Han Solo" :email "han@solo.net"})
                db/save-customer #(is (= "han.solo@rebels.net" (:email %1))]
              (update-customer-email "id" "han.solo@rebels.net"))))

Not a good test. It can't treat `update-customer-email` as a black-box and needs to understand what to re-define.

If `update-customer-email` uses a different `db` fn, the test will break.

{Make an onion} Refactoring techniques to turn your Clojure code into an onion WORK IN PROGRESS

Code

By Jochen Bedersdorfer

Code

2 years ago
247

Jochen Bedersdorfer

Software Engineer

beders

{Make an onion}

Onion?!?

Refactoring Techniques

Separate calculations from side-effects

Code

Code

Jochen Bedersdorfer

	(defn update-customer-email [customer-id new-email]
	(let [customer (-> (db/load-customer customer-id) ;; I/O
	(assoc :email (str/trim new-email))];; calculation
	(db/save-customer customer))) ;; I/O

	(deftest test-update-customer-email []
	(with-redefs [db/load-customer (constantly {:name "Han Solo" :email "han@solo.net"})
	db/save-customer #(is (= "han.solo@rebels.net" (:email %1))]
	(update-customer-email "id" "han.solo@rebels.net"))))

{Make an onion}

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