fixed test

app/Temperature/Temperature.php

+<?php
+
+namespace Sisoft\Temperature;
+
+use External\Service;
+
+class Temperature
+{
+    private $service;
+
+    public function __construct(Service $service)
+    {
+        $this->service = $service;
+    }
+
+    public function average()
+    {
+        $total = 0;
+        for ($i = 0; $i < 3; $i++) {
+            $total += $this->service->leerTemperatura();
+        }
+        return $total / 3;
+    }
+}

tests/OperacionesTests.php → tests/OperacionesTest.php

 <?php
+
 namespace Tests;
+
 use InvalidArgumentException;
 use PHPUnit\Framework\TestCase;
 use Sisoft\Calculadora\Operaciones;
 use Sisoft\Excepciones\MiPrimeraExcepcion;
 
 //TDD importante estudiar
-class OperacionesTests extends TestCase
+class OperacionesTest extends TestCase
 {
 
     private $op;

tests/TemperatureTest.php

+<?php
+
+namespace Tests;
+
+use \Mockery;
+use Sisoft\Temperature\Temperature;
+
+class TemperatureTest extends \PHPUnit\Framework\TestCase
+{
+    public function testGetsAverageTemperatureFromThreeServiceReadings()
+    {
+        $service = Mockery::mock('External\Service');
+
+        $service->shouldReceive('leerTemperatura')
+            ->times(3)
+            ->andReturn(12, 10, 14);
+
+        $temperature = new Temperature($service);
+
+        $this->assertEquals(12, $temperature->average());
+    }
+}