fix tests

Author: Baptouuuu

tests/Monoid/ConcatTest.php

@@ -14,12 +14,12 @@ class ConcatTest extends TestCase
 {
     public function testInterface()
     {
-        $this->assertInstanceOf(Monoid::class, new Concat);
+        $this->assertInstanceOf(Monoid::class, Concat::monoid);
     }
 
     public function testCombine()
     {
-        $str = (new Concat)->combine(Str::of('foo'), Str::of('bar'));
+        $str = Concat::monoid->combine(Str::of('foo'), Str::of('bar'));
 
         $this->assertInstanceOf(Str::class, $str);
         $this->assertSame(

tests/SequenceTest.php

@@ -852,12 +852,12 @@ public function testLazyMatch()
 
     public function testFold()
     {
-        $str = Sequence::of(Str::of('foo'), Str::of('bar'), Str::of('baz'))->fold(new Concat);
+        $str = Sequence::of(Str::of('foo'), Str::of('bar'), Str::of('baz'))->fold(Concat::monoid);
 
         $this->assertInstanceOf(Str::class, $str);
         $this->assertSame('foobarbaz', $str->toString());
 
-        $str = Sequence::of(Str::of('baz'), Str::of('foo'), Str::of('bar'))->fold(new Concat);
+        $str = Sequence::of(Str::of('baz'), Str::of('foo'), Str::of('bar'))->fold(Concat::monoid);
 
         $this->assertInstanceOf(Str::class, $str);
         $this->assertSame('bazfoobar', $str->toString());