From 3f111e317ac84be76733cfa71c4f5c171d5b601d Mon Sep 17 00:00:00 2001
From: widmogrod <widmogrod@gmail.com>
Date: Wed, 20 Dec 2017 18:30:46 +0100
Subject: [PATCH] Functional\join tests

---
 src/Functional/functions.php |  4 ++--
 test/Functional/JoinTest.php | 47 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 2 deletions(-)
 create mode 100644 test/Functional/JoinTest.php

diff --git a/src/Functional/functions.php b/src/Functional/functions.php
index d6772c0..f8aa857 100644
--- a/src/Functional/functions.php
+++ b/src/Functional/functions.php
@@ -197,13 +197,13 @@ function bind(callable $function = null, Monad $value = null)
 const join = 'Widmogrod\Functional\join';
 
 /**
- * join :: Monad (Monad m) -> Monad m
+ * join :: Monad m => m (m a) -> m a
  *
  * @param Monad $monad
  *
  * @return Monad
  */
-function join(Monad $monad = null)
+function join(Monad $monad): Monad
 {
     return $monad->bind(identity);
 }
diff --git a/test/Functional/JoinTest.php b/test/Functional/JoinTest.php
new file mode 100644
index 0000000..2afa1fe
--- /dev/null
+++ b/test/Functional/JoinTest.php
@@ -0,0 +1,47 @@
+<?php
+
+namespace test\Functional;
+
+use Widmogrod\FantasyLand\Monad;
+use function Widmogrod\Functional\flip;
+use const Widmogrod\Functional\identity;
+use function Widmogrod\Functional\join;
+use Widmogrod\Monad\Identity;
+use function Widmogrod\Monad\Maybe\just;
+use Widmogrod\Monad\State;
+
+class JoinTest extends \PHPUnit_Framework_TestCase
+{
+    /**
+     * @dataProvider provideData
+     */
+    public function test_it_should_remove_one_level_of_monadic_structure(
+        Monad $monad,
+        callable $run,
+        $expected
+    ) {
+        $result = join($monad);
+        $this->assertEquals($expected, $run($result));
+    }
+
+    public function provideData()
+    {
+        return [
+            'Just (Just 1)' => [
+                '$monad' => just(just(1)),
+                '$run' => identity,
+                '$value' => just(1),
+            ],
+            'Identity (Identity 1)' => [
+                '$monad' => Identity::of(Identity::of(2)),
+                '$run' => identity,
+                '$value' => Identity::of(2),
+            ],
+            'State (State 1)' => [
+                '$monad' => State\put(State\put(3)),
+                '$run' => flip(State\execState, 0),
+                '$value' => State\put(3),
+            ],
+        ];
+    }
+}
-- 
2.11.0