diff --git a/src/Accessor/FindAccessor.php b/src/Accessor/FindAccessor.php
index 268f45c..820fce6 100644
--- a/src/Accessor/FindAccessor.php
+++ b/src/Accessor/FindAccessor.php
@@ -14,7 +14,7 @@ class FindAccessor extends Accessor
      *
      * @param Collection $collection
      * @param callable   $iterator
-     * @return Collection
+     * @return bool
      */
     public function __invoke($collection, $iterator)
     {
diff --git a/src/Accessor/ValueAccessor.php b/src/Accessor/ValueAccessor.php
index 75cd51c..bb06c95 100644
--- a/src/Accessor/ValueAccessor.php
+++ b/src/Accessor/ValueAccessor.php
@@ -5,6 +5,9 @@
 use Underscore\Accessor;
 use Underscore\Collection;
 
+/**
+ * @deprecated Use toArray() instead. Will be removed in later releases
+ */
 class ValueAccessor extends Accessor
 {
     /**
diff --git a/src/Collection.php b/src/Collection.php
index f09ec8c..e059164 100644
--- a/src/Collection.php
+++ b/src/Collection.php
@@ -29,6 +29,7 @@ public function getIteratorReversed()
 
     /**
      * @return mixed
+     * @deprecated Use toArray() instead. Will be removed in later releases
      */
     public function value()
     {
diff --git a/tests/Accessor/AllAccessorTest.php b/tests/Accessor/AllAccessorTest.php
new file mode 100644
index 0000000..d46b9cb
--- /dev/null
+++ b/tests/Accessor/AllAccessorTest.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace Underscore\Test\Accessor;
+
+use Underscore\Accessor;
+use Underscore\Collection;
+
+class AllAccessorTest extends BaseAccessorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Accessor\AllAccessor();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $func = function ($value) {
+            return 3 <= strlen($value);
+        };
+        $ret = [];
+
+        $ret[] = [
+            true,
+            [new Collection($this->getDummy1()), $func],
+        ];
+
+        $ret[] = [
+            false,
+            [new Collection($this->getDummy2()), $func],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Accessor/AnyAccessorTest.php b/tests/Accessor/AnyAccessorTest.php
new file mode 100644
index 0000000..c610f8f
--- /dev/null
+++ b/tests/Accessor/AnyAccessorTest.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace Underscore\Test\Accessor;
+
+use Underscore\Accessor;
+use Underscore\Collection;
+
+class AnyAccessorTest extends BaseAccessorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Accessor\AnyAccessor();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $func = function ($value) {
+            return is_bool($value);
+        };
+        $ret = [];
+
+        $ret[] = [
+            false,
+            [new Collection($this->getDummy1()), $func],
+        ];
+
+        $ret[] = [
+            true,
+            [new Collection($this->getDummy2()), $func],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Accessor/BaseAccessorTest.php b/tests/Accessor/BaseAccessorTest.php
new file mode 100644
index 0000000..53dfa8a
--- /dev/null
+++ b/tests/Accessor/BaseAccessorTest.php
@@ -0,0 +1,91 @@
+<?php
+
+namespace Underscore\Test\Accessor;
+
+use Underscore\Accessor;
+
+abstract class BaseAccessorTest extends \PHPUnit_Framework_TestCase
+{
+    protected static function getDummy1()
+    {
+        $dummy = new \stdClass();
+        $dummy->name = 'dummy';
+        $dummy->foo = 'bar';
+        $dummy->baz = 'qux';
+
+        return $dummy;
+    }
+
+    /**
+     * @return object
+     */
+    protected static function getDummy2()
+    {
+        $dummy = self::getDummy1();
+        $dummy->false = false;
+        $dummy->null = null;
+        $dummy->zero = 0;
+
+        return $dummy;
+    }
+
+    protected static function getDummy3()
+    {
+        $dummy = [
+            'Angela' => [
+                'position' => 'dean',
+                'sex'      => 'female',
+            ],
+            'Bob'    => [
+                'position' => 'janitor',
+                'sex'      => 'male',
+            ],
+            'Mark'   => [
+                'position' => 'teacher',
+                'sex'      => 'male',
+                'tenured'  => true,
+            ],
+            'Wendy'  => [
+                'position' => 'teacher',
+                'sex'      => 'female',
+                'tenured'  => 1,
+            ],
+        ];
+
+        return $dummy;
+    }
+
+
+    /**
+     * @return object
+     */
+    protected static function getDummy4()
+    {
+        $dummy = self::getDummy2();
+        $dummy->false = false;
+        $dummy->null = null;
+        $dummy->zero = 0;
+        $dummy->one = 1;
+
+        return $dummy;
+    }
+    /**
+     * @return Accessor|callable
+     */
+    abstract protected function getInstance();
+
+    /**
+     * @return mixed[]
+     */
+    abstract protected function getTestInvokeData();
+
+    /**
+     * @param mixed $expected
+     * @param mixed $args
+     * @dataProvider getTestInvokeData
+     */
+    public function testInvoke($expected, $args)
+    {
+        $this->assertSame($expected, call_user_func_array($this->getInstance(), $args));
+    }
+}
diff --git a/tests/Accessor/ContainsAccessorTest.php b/tests/Accessor/ContainsAccessorTest.php
new file mode 100644
index 0000000..0d801fc
--- /dev/null
+++ b/tests/Accessor/ContainsAccessorTest.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace Underscore\Test\Accessor;
+
+use Underscore\Accessor;
+use Underscore\Collection;
+
+class ContainsAccessorTest extends BaseAccessorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Accessor\ContainsAccessor();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            true,
+            [new Collection($this->getDummy1()), 'bar'],
+        ];
+
+        $ret[] = [
+            false,
+            [new Collection($this->getDummy1()), 'baz'],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Accessor/FindAccessorTest.php b/tests/Accessor/FindAccessorTest.php
new file mode 100644
index 0000000..136a82b
--- /dev/null
+++ b/tests/Accessor/FindAccessorTest.php
@@ -0,0 +1,43 @@
+<?php
+
+namespace Underscore\Test\Accessor;
+
+use Underscore\Accessor;
+use Underscore\Collection;
+
+class FindAccessorTest extends BaseAccessorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Accessor\FindAccessor();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $func = function ($needle) {
+            return function ($value) use ($needle) {
+                return $value === $needle;
+            };
+        };
+
+        $ret = [];
+
+        $ret[] = [
+            false,
+            [new Collection($this->getDummy1()), $func('foo')],
+        ];
+
+        $ret[] = [
+            true,
+            [new Collection($this->getDummy1()), $func('bar')],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Accessor/HasAccessorTest.php b/tests/Accessor/HasAccessorTest.php
new file mode 100644
index 0000000..5d3874a
--- /dev/null
+++ b/tests/Accessor/HasAccessorTest.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace Underscore\Test\Accessor;
+
+use Underscore\Accessor;
+use Underscore\Collection;
+
+class HasAccessorTest extends BaseAccessorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Accessor\HasAccessor();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            true,
+            [new Collection($this->getDummy1()), 'foo'],
+        ];
+
+        $ret[] = [
+            false,
+            [new Collection($this->getDummy1()), 'bar'],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Accessor/MaxAccessorTest.php b/tests/Accessor/MaxAccessorTest.php
new file mode 100644
index 0000000..e7bb8a2
--- /dev/null
+++ b/tests/Accessor/MaxAccessorTest.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace Underscore\Test\Accessor;
+
+use Underscore\Accessor;
+use Underscore\Collection;
+
+class MaxAccessorTest extends BaseAccessorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Accessor\MaxAccessor();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            2,
+            [new Collection([0, 1, 2])],
+        ];
+
+        $ret[] = [
+            0,
+            [new Collection([0, false, 'foo'])],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Accessor/MinAccessorTest.php b/tests/Accessor/MinAccessorTest.php
new file mode 100644
index 0000000..add866f
--- /dev/null
+++ b/tests/Accessor/MinAccessorTest.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace Underscore\Test\Accessor;
+
+use Underscore\Accessor;
+use Underscore\Collection;
+
+class MinAccessorTest extends BaseAccessorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Accessor\MinAccessor();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            0,
+            [new Collection([0, 1, 2])],
+        ];
+
+        $ret[] = [
+            0,
+            [new Collection([0, false, 'foo'])],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Accessor/ReduceAccessorTest.php b/tests/Accessor/ReduceAccessorTest.php
new file mode 100644
index 0000000..89cfdd3
--- /dev/null
+++ b/tests/Accessor/ReduceAccessorTest.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace Underscore\Test\Accessor;
+
+use Underscore\Accessor;
+use Underscore\Collection;
+
+class ReduceAccessorTest extends BaseAccessorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Accessor\ReduceAccessor();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $func = function ($accu, $value) {
+            $accu .= $value . ' ';
+
+            return $accu;
+        };
+        $ret = [];
+
+        $ret[] = [
+            'dummy bar qux ',
+            [new Collection($this->getDummy1()), $func],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Accessor/ReduceRightAccessorTest.php b/tests/Accessor/ReduceRightAccessorTest.php
new file mode 100644
index 0000000..f831fe3
--- /dev/null
+++ b/tests/Accessor/ReduceRightAccessorTest.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace Underscore\Test\Accessor;
+
+use Underscore\Accessor;
+use Underscore\Collection;
+
+class ReduceRightAccessorTest extends BaseAccessorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Accessor\ReduceRightAccessor();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $func = function ($accu, $value) {
+            $accu .= $value . ' ';
+
+            return $accu;
+        };
+        $ret = [];
+
+        $ret[] = [
+            'qux bar dummy ',
+            [new Collection($this->getDummy1()), $func],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Accessor/SizeAccessorTest.php b/tests/Accessor/SizeAccessorTest.php
new file mode 100644
index 0000000..ae2c520
--- /dev/null
+++ b/tests/Accessor/SizeAccessorTest.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace Underscore\Test\Accessor;
+
+use Underscore\Accessor;
+use Underscore\Collection;
+
+class SizeAccessorTest extends BaseAccessorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Accessor\SizeAccessor();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            3,
+            [new Collection($this->getDummy1())],
+        ];
+
+        $ret[] = [
+            6,
+            [new Collection($this->getDummy2())],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Accessor/ToArrayAccessorTest.php b/tests/Accessor/ToArrayAccessorTest.php
new file mode 100644
index 0000000..372a704
--- /dev/null
+++ b/tests/Accessor/ToArrayAccessorTest.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace Underscore\Test\Accessor;
+
+use Underscore\Accessor;
+use Underscore\Collection;
+
+class ToArrayAccessorTest extends BaseAccessorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Accessor\ToArrayAccessor();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            (array) $this->getDummy1(),
+            [new Collection($this->getDummy1())],
+        ];
+
+        $ret[] = [
+            (array) $this->getDummy2(),
+            [new Collection($this->getDummy2())],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Accessor/ValueAccessorTest.php b/tests/Accessor/ValueAccessorTest.php
new file mode 100644
index 0000000..9383afb
--- /dev/null
+++ b/tests/Accessor/ValueAccessorTest.php
@@ -0,0 +1,37 @@
+<?php
+
+namespace Underscore\Test\Accessor;
+
+use Underscore\Accessor;
+use Underscore\Collection;
+
+class ValueAccessorTest extends BaseAccessorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Accessor\ValueAccessor();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            (array) $this->getDummy1(),
+            [new Collection($this->getDummy1())],
+        ];
+
+        $ret[] = [
+            (array) $this->getDummy2(),
+            [new Collection($this->getDummy2())],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/BaseMutatorTest.php b/tests/Mutator/BaseMutatorTest.php
new file mode 100644
index 0000000..1edc023
--- /dev/null
+++ b/tests/Mutator/BaseMutatorTest.php
@@ -0,0 +1,91 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Mutator;
+
+abstract class BaseMutatorTest extends \PHPUnit_Framework_TestCase
+{
+    protected static function getDummy1()
+    {
+        $dummy = new \stdClass();
+        $dummy->name = 'dummy';
+        $dummy->foo = 'bar';
+        $dummy->baz = 'qux';
+
+        return $dummy;
+    }
+
+    /**
+     * @return object
+     */
+    protected static function getDummy2()
+    {
+        $dummy = self::getDummy1();
+        $dummy->false = false;
+        $dummy->null = null;
+        $dummy->zero = 0;
+
+        return $dummy;
+    }
+
+    protected static function getDummy3()
+    {
+        $dummy = [
+            'Angela' => [
+                'position' => 'dean',
+                'sex'      => 'female',
+            ],
+            'Bob'    => [
+                'position' => 'janitor',
+                'sex'      => 'male',
+            ],
+            'Mark'   => [
+                'position' => 'teacher',
+                'sex'      => 'male',
+                'tenured'  => true,
+            ],
+            'Wendy'  => [
+                'position' => 'teacher',
+                'sex'      => 'female',
+                'tenured'  => 1,
+            ],
+        ];
+
+        return $dummy;
+    }
+
+
+    /**
+     * @return object
+     */
+    protected static function getDummy4()
+    {
+        $dummy = self::getDummy2();
+        $dummy->false = false;
+        $dummy->null = null;
+        $dummy->zero = 0;
+        $dummy->one = 1;
+
+        return $dummy;
+    }
+    /**
+     * @return Mutator|callable
+     */
+    abstract protected function getInstance();
+
+    /**
+     * @return mixed[]
+     */
+    abstract public function getTestInvokeData();
+
+    /**
+     * @param mixed $expected
+     * @param mixed $args
+     * @dataProvider getTestInvokeData
+     */
+    public function testInvoke($expected, $args)
+    {
+        $this->assertSame($expected, call_user_func_array($this->getInstance(), $args)->toArray());
+    }
+}
diff --git a/tests/Mutator/FilterMutatorTest.php b/tests/Mutator/FilterMutatorTest.php
new file mode 100644
index 0000000..f70c065
--- /dev/null
+++ b/tests/Mutator/FilterMutatorTest.php
@@ -0,0 +1,36 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class FilterMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\FilterMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $func = function ($value) {
+            return 3 < strlen($value);
+        };
+
+        $ret = [];
+
+        $ret[] = [
+            ['name' => 'dummy'],
+            [new Collection($this->getDummy1()), $func],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/GroupByMutatorTest.php b/tests/Mutator/GroupByMutatorTest.php
new file mode 100644
index 0000000..aa61a92
--- /dev/null
+++ b/tests/Mutator/GroupByMutatorTest.php
@@ -0,0 +1,35 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class GroupByMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\GroupByMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            [
+                5 => ['dummy'],
+                3 => ['bar', 'qux'],
+            ],
+            [new Collection($this->getDummy1()), 'strlen'],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/HeadMutatorTest.php b/tests/Mutator/HeadMutatorTest.php
new file mode 100644
index 0000000..3de26d0
--- /dev/null
+++ b/tests/Mutator/HeadMutatorTest.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class HeadMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\HeadMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            ['name' => 'dummy', 'foo' => 'bar'],
+            [new Collection($this->getDummy1()), 2],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/InitialMutatorTest.php b/tests/Mutator/InitialMutatorTest.php
new file mode 100644
index 0000000..9dcbfea
--- /dev/null
+++ b/tests/Mutator/InitialMutatorTest.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class InitialMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\InitialMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            ['name' => 'dummy'],
+            [new Collection($this->getDummy1()), 2],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/KeysMutatorTest.php b/tests/Mutator/KeysMutatorTest.php
new file mode 100644
index 0000000..d78b95d
--- /dev/null
+++ b/tests/Mutator/KeysMutatorTest.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class KeysMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\KeysMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            ['name', 'foo', 'baz'],
+            [new Collection($this->getDummy1())],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/LastMutatorTest.php b/tests/Mutator/LastMutatorTest.php
new file mode 100644
index 0000000..35b09ed
--- /dev/null
+++ b/tests/Mutator/LastMutatorTest.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class LastMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\LastMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            ['foo' => 'bar', 'baz' => 'qux'],
+            [new Collection($this->getDummy1()), 2],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/MapMutatorTest.php b/tests/Mutator/MapMutatorTest.php
new file mode 100644
index 0000000..2195025
--- /dev/null
+++ b/tests/Mutator/MapMutatorTest.php
@@ -0,0 +1,36 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class MapMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\MapMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $func = function ($value, $key) {
+            return sprintf('%s:%s', $key, $value);
+        };
+
+        $ret = [];
+
+        $ret[] = [
+            ['name' => 'name:dummy', 'foo' => 'foo:bar', 'baz' => 'baz:qux'],
+            [new Collection($this->getDummy1()), $func],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/MergeMutatorTest.php b/tests/Mutator/MergeMutatorTest.php
new file mode 100644
index 0000000..18b3f30
--- /dev/null
+++ b/tests/Mutator/MergeMutatorTest.php
@@ -0,0 +1,39 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class MergeMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\MergeMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            [
+                'name'  => 'dummy',
+                'foo'   => 'bar',
+                'baz'   => 'qux',
+                'false' => false,
+                'null'  => null,
+                'zero'  => 0,
+            ],
+            [new Collection($this->getDummy1()), new Collection($this->getDummy2())],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/PickMutatorTest.php b/tests/Mutator/PickMutatorTest.php
new file mode 100644
index 0000000..9722c1d
--- /dev/null
+++ b/tests/Mutator/PickMutatorTest.php
@@ -0,0 +1,38 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+use Underscore\Test\Dummy;
+
+class PickMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\PickMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            ['bar', 'bar'],
+            [new Collection([$this->getDummy1(), $this->getDummy1()]), 'foo'],
+        ];
+
+        $ret[] = [
+            ['foo'],
+            [new Collection([new Dummy()]), 'getFoo'],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/RejectMutatorTest.php b/tests/Mutator/RejectMutatorTest.php
new file mode 100644
index 0000000..23c90b7
--- /dev/null
+++ b/tests/Mutator/RejectMutatorTest.php
@@ -0,0 +1,36 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class RejectMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\RejectMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $func = function ($value) {
+            return 3 < strlen($value);
+        };
+
+        $ret = [];
+
+        $ret[] = [
+            ['foo' => 'bar', 'baz' => 'qux'],
+            [new Collection($this->getDummy1()), $func],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/SortByMutatorTest.php b/tests/Mutator/SortByMutatorTest.php
new file mode 100644
index 0000000..45d6468
--- /dev/null
+++ b/tests/Mutator/SortByMutatorTest.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class SortByMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\SortByMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            ['bar', 'qux', 'dummy',],
+            [new Collection($this->getDummy1()), 'strlen'],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/TailMutatorTest.php b/tests/Mutator/TailMutatorTest.php
new file mode 100644
index 0000000..d468c73
--- /dev/null
+++ b/tests/Mutator/TailMutatorTest.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class TailMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\TailMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            ['foo' => 'bar', 'baz' => 'qux'],
+            [new Collection($this->getDummy1()), 1],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/ValuesMutatorTest.php b/tests/Mutator/ValuesMutatorTest.php
new file mode 100644
index 0000000..865f108
--- /dev/null
+++ b/tests/Mutator/ValuesMutatorTest.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class ValuesMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\ValuesMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            ['dummy', 'bar', 'qux'],
+            [new Collection($this->getDummy1())],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/WithoutMutatorTest.php b/tests/Mutator/WithoutMutatorTest.php
new file mode 100644
index 0000000..265df36
--- /dev/null
+++ b/tests/Mutator/WithoutMutatorTest.php
@@ -0,0 +1,32 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class WithoutMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\WithoutMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            ['foo' => 'bar', 'baz' => 'qux'],
+            [new Collection($this->getDummy1()), ['dummy']],
+        ];
+
+        return $ret;
+    }
+}
diff --git a/tests/Mutator/ZipMutatorTest.php b/tests/Mutator/ZipMutatorTest.php
new file mode 100644
index 0000000..5e75ef5
--- /dev/null
+++ b/tests/Mutator/ZipMutatorTest.php
@@ -0,0 +1,44 @@
+<?php
+
+namespace Underscore\Test\Mutator;
+
+use Underscore\Collection;
+use Underscore\Mutator;
+
+class ZipMutatorTest extends BaseMutatorTest
+{
+    /**
+     * @inheritDoc
+     */
+    protected function getInstance()
+    {
+        return new Mutator\ZipMutator();
+    }
+
+    /**
+     * @inheritDoc
+     */
+    public function getTestInvokeData()
+    {
+        $ret = [];
+
+        $ret[] = [
+            [
+                'a'  => 'dummy',
+                1    => 'bar',
+                '42' => 'qux',
+            ],
+            [new Collection($this->getDummy1()), ['a', 1, '42']],
+        ];
+
+        return $ret;
+    }
+
+    /**
+     * @expectedException \LogicException
+     */
+    public function testThrowIfWrongDimmensions()
+    {
+        $this->getInstance()->__invoke(new Collection($this->getDummy1()), ['a']);
+    }
+}
diff --git a/tests/UnderscoreTest.php b/tests/UnderscoreTest.php
index ec8a775..951eb02 100644
--- a/tests/UnderscoreTest.php
+++ b/tests/UnderscoreTest.php
@@ -106,12 +106,6 @@ public function testRange($start, $stop, $step, $expected, $exception = null)
         );
     }
 
-    public function testValue()
-    {
-        $value = Underscore::from($this->getDummy())->value();
-        $this->assertEquals((array)$this->getDummy(), $value);
-    }
-
     public function testInvoke()
     {
         $buffer = '';
@@ -124,198 +118,6 @@ function ($value, $key) use (&$buffer) {
         $this->assertSame('name:dummy|foo:bar|baz:qux|', $buffer);
     }
 
-    public function testMap()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->map(
-                function ($value, $key) use (&$buffer) {
-                    return sprintf('%s:%s', $key, $value);
-                }
-            )->toArray();
-
-        $this->assertSame(
-            ['name' => 'name:dummy', 'foo' => 'foo:bar', 'baz' => 'baz:qux'],
-            $value
-        );
-    }
-
-    public function testReduce()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->reduce(
-                function ($accu, $value) {
-                    $accu .= $value . ' ';
-
-                    return $accu;
-                },
-                ''
-            );
-
-        $this->assertSame('dummy bar qux ', $value);
-    }
-
-    public function testReduceRight()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->reduceRight(
-                function ($accumulator, $value) {
-                    $accumulator .= $value . ' ';
-
-                    return $accumulator;
-                },
-                ''
-            );
-
-        $this->assertSame('qux bar dummy ', $value);
-    }
-
-    public function testPick()
-    {
-        $value = Underscore::from([$this->getDummy(), $this->getDummy(), $this->getDummy()])
-            ->pick('foo')
-            ->toArray();
-
-        $this->assertSame(['bar', 'bar', 'bar'], $value);
-    }
-
-    public function testPickGetter()
-    {
-        $value = Underscore::from([new Dummy()])
-            ->pick('getFoo')
-            ->toArray();
-
-        $this->assertSame(['foo'], $value);
-    }
-
-    public function testContains()
-    {
-        $this->assertTrue(Underscore::from($this->getDummy())->contains('bar'));
-        $this->assertFalse(Underscore::from($this->getDummy())->contains('baz'));
-    }
-
-    public function testFind()
-    {
-        $iterator = function ($needle) {
-            return function ($value) use ($needle) {
-                return $value === $needle;
-            };
-        };
-        $this->assertTrue(Underscore::from($this->getDummy())->find($iterator('bar')));
-        $this->assertFalse(Underscore::from($this->getDummy())->find($iterator('foo')));
-    }
-
-    public function testFilter()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->filter(
-                function ($value) {
-                    return 3 < strlen($value);
-                }
-            )
-            ->toArray();
-
-        $this->assertSame(['name' => 'dummy'], $value);
-    }
-
-    public function testReject()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->reject(
-                function ($value) {
-                    return 3 < strlen($value);
-                }
-            )
-            ->toArray();
-
-        $this->assertSame(['foo' => 'bar', 'baz' => 'qux'], $value);
-    }
-
-    public function testAny()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->any(
-                function ($value) {
-                    return 3 < strlen($value);
-                }
-            );
-
-        $this->assertSame(true, $value);
-
-        $value = Underscore::from($this->getDummy())
-            ->any(
-                function ($value) {
-                    return strlen($value) < 2;
-                }
-            );
-
-        $this->assertSame(false, $value);
-    }
-
-    public function testAll()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->all(
-                function ($value) {
-                    return 3 <= strlen($value);
-                }
-            );
-
-        $this->assertSame(true, $value);
-
-        $value = Underscore::from($this->getDummy())
-            ->all(
-                function ($value) {
-                    return 3 < strlen($value);
-                }
-            );
-
-        $this->assertSame(false, $value);
-    }
-
-    public function testSize()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->size();
-
-        $this->assertSame(3, $value);
-    }
-
-    public function testHead()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->head(2)
-            ->value();
-
-        $this->assertSame(['name' => 'dummy', 'foo' => 'bar'], $value);
-    }
-
-    public function testTail()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->tail(1)
-            ->value();
-
-        $this->assertSame(['foo' => 'bar', 'baz' => 'qux'], $value);
-    }
-
-    public function testInitial()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->initial(2)
-            ->value();
-
-        $this->assertSame(['name' => 'dummy'], $value);
-    }
-
-    public function testLast()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->last(2)
-            ->value();
-
-        $this->assertSame(['foo' => 'bar', 'baz' => 'qux'], $value);
-    }
-
     public function testCompact()
     {
         $value = Underscore::from($this->getDummy2())
@@ -325,78 +127,6 @@ public function testCompact()
         $this->assertSame(['name' => 'dummy', 'foo' => 'bar', 'baz' => 'qux'], $value);
     }
 
-    public function testWithout()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->without(['dummy'])
-            ->toArray();
-
-        $this->assertSame(['foo' => 'bar', 'baz' => 'qux'], $value);
-    }
-
-    public function testMerge()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->merge(new Collection($this->getDummy2()))
-            ->toArray();
-
-        $this->assertSame(
-            [
-                'name'  => 'dummy',
-                'foo'   => 'bar',
-                'baz'   => 'qux',
-                'false' => false,
-                'null'  => null,
-                'zero'  => 0,
-            ],
-            $value
-        );
-    }
-
-    public function testValues()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->values()
-            ->toArray();
-
-        $this->assertSame(
-            [
-                'dummy',
-                'bar',
-                'qux',
-            ],
-            $value
-        );
-    }
-
-    public function testKeys()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->keys()
-            ->toArray();
-
-        $this->assertSame(
-            [
-                'name',
-                'foo',
-                'baz',
-            ],
-            $value
-        );
-    }
-
-    public function testHas()
-    {
-        $collection = Underscore::from($this->getDummy());
-
-        $this->assertTrue($collection->has('name'));
-        $this->assertTrue($collection->has('foo'));
-        $this->assertTrue($collection->has('baz'));
-
-        $this->assertFalse($collection->has('nope'));
-        $this->assertFalse($collection->has('missing'));
-    }
-
     public function testClone()
     {
         $original = $this->getDummy();
@@ -411,57 +141,6 @@ public function testClone()
         );
     }
 
-    public function testZip()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->zip(['a', 1, '42'])
-            ->toArray();
-
-        $this->assertSame(
-            [
-                'a'  => 'dummy',
-                1    => 'bar',
-                '42' => 'qux',
-            ],
-            $value
-        );
-
-        $this->setExpectedException('\LogicException');
-        Underscore::from($this->getDummy())
-            ->zip(['a']);
-    }
-
-    public function testGroupBy()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->groupBy('strlen')
-            ->toArray();
-
-        $this->assertSame(
-            [
-                5 => ['dummy'],
-                3 => ['bar', 'qux'],
-            ],
-            $value
-        );
-    }
-
-    public function testSortBy()
-    {
-        $value = Underscore::from($this->getDummy())
-            ->sortBy('strlen')
-            ->toArray();
-
-        $this->assertSame(
-            [
-                'bar',
-                'qux',
-                'dummy',
-            ],
-            $value
-        );
-    }
-
     /**
      * @return array
      */