TDD Kata Recent Song-listλ︎
Create a recent song list to hold a unique set of songs that have been played.
The most recently played song is at the start of the list, the least recently played song is the last in the list.
- A recently-used-list is initially empty.
- Songs in the list are unique, so repeatedly played songs should only appear once in the list
- Songs can be looked up by index, which counts from zero.
- The song list can be transitory (starting from empty each time) or persistent within a REPL session (examples use a transitory approach)
Optional extras:
- Empty song names are not allowed.
- Add a limit to the number of songs the list contains, with the least recently added items dropped when that limit is reached.
Create Projectλ︎
Create a new project using clj-new
Run REPLλ︎
Start a Clojure REPL via a Clojure editor or via the command line from the root of the project directory
Unit Testsλ︎
clojure.test library is part of Clojure standard library and is the most common way to write unit tests in Clojure
Open test/playground/song_list_test.clj file in your editor and update the namespace definition to include clojure.test
Require clojure.test namespace
Run Testsλ︎
Evaluate the practicalli.song-list and practicalli.song-list-test namespaces to load their code into the REPL
Call the run-tests function in the REPL to get a report back on all of the tests in our current namespace (song-list)
Practicall Clojure CLI Config provides the :test/run alias to run the Kaocha test runner.
Kaocha test runner
Open a command line in the root directory of the project and run the following command.
Kaocha runs all the tests, stopping should a test fail.
Test song-list existsλ︎
Write a test to see if a recent song list exists.
This is an opportunity to think about what kind of data structure you want to use to hold your recent song list.
Try write the code first and then check that code with the examples provided (click to expand each code example box)
Test song-list exists
A simple test that checks for a recent-songs list
(deftest song-list-exists-test
(testing "Does a recent song list exist"
(is (vector? song-list/recent-songs))))
recent-songs should be defined in src/playground/recent-song-list.clj before running the test, otherwise a compilation error will be returned.
Define a recent song listλ︎
Edit src/playground/song_list.clj and define a name for the collection of recent songs
Use an empty collection to start with. Which collection type will you use though (hash-map {}, list (), set #{}, vector [])?
recent-songs collection
Define a recent-song name for an empty vector
Test First Approach
For a strict test first approach, a recent-songs name (symbol) would be defined that returns false or a falsy value, e.g. nil
A name (symbol) must be defined for use in the test so that the Clojure code can compile
Test song-list is emptyλ︎
The recent song list should be empty to start with.
Check song list is empty
A simple test that compares an empty vector with the value of recent-songs
(deftest song-list-empty-test
(testing "Is song list empty if we haven't added any songs"
(is
(= [] song-list/recent-songs))))
Here is the same test using the empty? function instead of the = function.
Test adding a song to the listλ︎
Add a song to the collection, for example Tubular Bells - Mike Oldfield
Test adding a song to the list
(deftest add-songs-test
(testing "add song returns a song list with entries"
(is
(not (empty?
(add-song "Barry Manilow - Love on the rocks" song-list/recent-songs)))))
(testing "add multiple song returns a song list with entries"
(is
(not (empty?
(->> song-list/recent-songs
(add-song "Mike Oldfield - Tubular Bells Part 1")
(add-song "Barry Manilow - Love on the rocks")
(add-song "Phil Colins - Sususudio" )))))))
Other songs are avialbe and Practicalli makes no recommendation as to what songs should be used or listened too.
Function to add songλ︎
Create a function to add a song to the start of the song list.
Function to add song to list
The add-song function takes the name of a song and the song list to which it will be added.
A Thread-last macro ->> is used to pass the song list over two functions.
The song-list is first passed to the remove expression as its last argument. This expression will remove any occurrence of the new song we want to add from the song-list.
The results of the remove expression are then passed to the cons expression as its last argument. The cons expression simply adds the new song to the start of the list, making it the most recent song.
(def recent-songs [])
(defn add-song [song song-list]
(cons song song-list))
recent-songs is passed into the add-song function as an argument, song-list to keep the design of add-song function pure (no side-effects). This design also provides greater scope to using the add-song function, as any song list can be added to, rather than hard-coding recent-songs list.
Test song added to top of listλ︎
As the song list shows recently played songs, new songs added should be at the top of the list.
The list should not contain duplicate entries for a song.
Test songs added to top of list
(deftest recently-added-song-first-test
(testing "most recent song should be first in the list when empty list"
(is (=
(first (add-song "Daft Punk - Get Lucky" recent-songs))
"Daft Punk - Get Lucky")))
(testing "most recent song should be first in list when adding multiple songs"
(is (=
(first
(->> recent-songs
(add-song "Daft Punk - Get Lucky")
(add-song "Pharrell Williams - Happy")))
"Pharrell Williams - Happy")))
(testing "most recent song should be first in list when adding a repeated song"
(is (=
(first
(->> recent-songs
(add-song "Pharrell Williams - Happy")
(add-song "Daft Punk - Get Lucky")
(add-song "Pharrell Williams - Happy")))
"Pharrell Williams - Happy")))
(testing "most recent song should be first in list when adding a repeated song"
(is (not=
(last
(->> recent-songs
(add-song "Pharrell Williams - Happy")
(add-song "Daft Punk - Get Lucky")
(add-song "Pharrell Williams - Happy")))
"Pharrell Williams - Happy"))))
Add song to start of listλ︎
Create a function to add a song to the start of the song list.
Function to add song to list
The add-song function takes the name of a song and the song list to which it will be added.
A Thread-last macro ->> is used to pass the song list over two functions.
The song-list is first passed to the remove expression as its last argument. This expression will remove any occurrence of the new song we want to add from the song-list.
The results of the remove expression are then passed to the cons expression as its last argument. The cons expression simply adds the new song to the start of the list, making it the most recent song.
(def recent-songs [])
(defn add-song [song song-list]
(->> song-list
(remove #(= song %))
(cons song)))
recent-songs is passed into the add-song function as an argument, song-list to keep the design of add-song function pure (no side-effects). This design also provides greater scope to using the add-song function, as any song list can be added to, rather than hard-coding recent-songs list.