diff --git a/exercises/accumulate/example.php b/exercises/accumulate/example.php
index b1b571bb9..98cf14e3c 100644
--- a/exercises/accumulate/example.php
+++ b/exercises/accumulate/example.php
@@ -1,11 +1,13 @@
 <?php
 
+namespace Exercism\Accumulate;
+
 /**
  * Given the input array and operation returns an array
  * containing the result of applying that operation
  * to each element of the input array.
  *
- * @param array    $input
+ * @param array $input
  * @param callable $accumulator
  *
  * @return array
diff --git a/exercises/accumulate/accumulate.php b/exercises/accumulate/src/accumulate.php
similarity index 74%
rename from exercises/accumulate/accumulate.php
rename to exercises/accumulate/src/accumulate.php
index f1e2100cf..a2cfccdc5 100644
--- a/exercises/accumulate/accumulate.php
+++ b/exercises/accumulate/src/accumulate.php
@@ -1,5 +1,7 @@
 <?php
 
+namespace Exercism\Accumulate;
+
 function accumulate(array $input, callable $accumulator)
 {
     // YOUR CODE GOES HERE
diff --git a/exercises/accumulate/accumulate_test.php b/exercises/accumulate/test/AccumulateTest.php
similarity index 80%
rename from exercises/accumulate/accumulate_test.php
rename to exercises/accumulate/test/AccumulateTest.php
index cde058864..b84e142d0 100644
--- a/exercises/accumulate/accumulate_test.php
+++ b/exercises/accumulate/test/AccumulateTest.php
@@ -1,10 +1,24 @@
 <?php
 
-class AccumulateTest extends PHPUnit\Framework\TestCase
+namespace ExercismTest\Accumulate;
+
+use PHPUnit\Framework\TestCase;
+use function Exercism\Accumulate\accumulate;
+
+class AccumulateTest extends TestCase
 {
     public static function setUpBeforeClass() : void
     {
-        require_once 'accumulate.php';
+        $files = [
+            '../src/accumulate.php',
+            'Str.php',
+            'StrSplitter.php',
+            'Is.php',
+        ];
+
+        foreach ($files as $file) {
+            require_once __DIR__ . '/' . $file;
+        }
     }
 
     public function testAccumulateEmpty() : void
@@ -54,15 +68,15 @@ public function testAccumulateConstants() : void
 
     public function testAccumulateWithinAccumulate() : void
     {
-        $chars = ['a', 'b', 'c'];
-        $digits = [1, 2, 3];
+        $chars    = ['a', 'b', 'c'];
+        $digits   = [1, 2, 3];
         $expected = [['a1', 'a2', 'a3'], ['b1', 'b2', 'b3'], ['c1', 'c2', 'c3']];
 
         $this->assertEquals(
             $expected,
             accumulate($chars, function ($char) use ($digits) {
                 return accumulate($digits, function ($digit) use ($char) {
-                    return $char.$digit;
+                    return $char . $digit;
                 });
             })
         );
@@ -77,12 +91,12 @@ public function testAccumulateUsingBuiltInFunction() : void
 
     public function testAccumulateUsingStaticMethod() : void
     {
-        $this->assertEquals([5, 6], accumulate(['Hello', 'World!'], 'Str::len'));
+        $this->assertEquals([5, 6], accumulate(['Hello', 'World!'], 'ExercismTest\Accumulate\Str::len'));
     }
 
     public function testAccumulateUsingInvoke() : void
     {
-        $this->assertEquals([['f', 'o', 'o']], accumulate(['foo'], new StrSpliter()));
+        $this->assertEquals([['f', 'o', 'o']], accumulate(['foo'], new StrSplitter()));
     }
 
     public function testAccumulateUsingObjectAndArrayNotation() : void
@@ -90,27 +104,3 @@ public function testAccumulateUsingObjectAndArrayNotation() : void
         $this->assertEquals([true, false, false], accumulate(['Yes', 0, []], [new Is(), 'truthy']));
     }
 }
-
-class Str
-{
-    public static function len($string) : int
-    {
-        return strlen($string);
-    }
-}
-
-class StrSpliter
-{
-    public function __invoke($value)
-    {
-        return str_split($value);
-    }
-}
-
-class Is
-{
-    public function truthy($value) : bool
-    {
-        return $value ? true : false;
-    }
-}
diff --git a/exercises/accumulate/test/Is.php b/exercises/accumulate/test/Is.php
new file mode 100644
index 000000000..970d2f6c3
--- /dev/null
+++ b/exercises/accumulate/test/Is.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace ExercismTest\Accumulate;
+
+class Is
+{
+    public function truthy($value): bool
+    {
+        return $value ? true : false;
+    }
+}
diff --git a/exercises/accumulate/test/Str.php b/exercises/accumulate/test/Str.php
new file mode 100644
index 000000000..b03a6ebca
--- /dev/null
+++ b/exercises/accumulate/test/Str.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace ExercismTest\Accumulate;
+
+class Str
+{
+    public static function len($string): int
+    {
+        return strlen($string);
+    }
+}
diff --git a/exercises/accumulate/test/StrSplitter.php b/exercises/accumulate/test/StrSplitter.php
new file mode 100644
index 000000000..b3eb376d9
--- /dev/null
+++ b/exercises/accumulate/test/StrSplitter.php
@@ -0,0 +1,11 @@
+<?php
+
+namespace ExercismTest\Accumulate;
+
+class StrSplitter
+{
+    public function __invoke($value)
+    {
+        return str_split($value);
+    }
+}