Add void return type

UPGRADE.md

@@ -33,7 +33,7 @@ The `SpeedTrap` Extension must be registered differently in `phpunit.xml`:
 If you have extended the old `JohnKary\PHPUnit\Listener\SpeedTrapListener`, you
 must extend the new `JohnKary\PHPUnit\Extension\SpeedTrap`. There are various
 method name changes that may affect your custom subclass. See [PR #83](https://github.com/johnkary/phpunit-speedtrap/pull/83)
-for how the new class has changed.
+for many of the new class has changed.
 
 UPGRADE FROM 3.x to 4.0
 =======================

src/SpeedTrap.php

@@ -124,7 +124,7 @@ protected function isSlow(int $time, int $slowThreshold): bool
      *
      * @param int $time Test execution time that was considered slow, in milliseconds
      */
-    protected function addSlowTest(string $test, int $time)
+    protected function addSlowTest(string $test, int $time): void
     {
         $label = $this->makeLabel($test);
 
@@ -193,15 +193,15 @@ protected function getHiddenCount(): int
     /**
      * Renders slowness report header.
      */
-    protected function renderHeader()
+    protected function renderHeader(): void
     {
         echo sprintf("\n\nYou should really speed up these slow tests (>%sms)...\n", $this->slowThreshold);
     }
 
     /**
      * Renders slowness report body.
      */
-    protected function renderBody()
+    protected function renderBody(): void
     {
         $slowTests = $this->slow;
 
@@ -217,7 +217,7 @@ protected function renderBody()
     /**
      * Renders slowness report footer.
      */
-    protected function renderFooter()
+    protected function renderFooter(): void
     {
         if ($hidden = $this->getHiddenCount()) {
             printf("...and there %s %s more above your threshold hidden from view\n", $hidden == 1 ? 'is' : 'are', $hidden);
@@ -227,7 +227,7 @@ protected function renderFooter()
     /**
      * Populate options into class internals.
      */
-    protected function loadOptions(array $options)
+    protected function loadOptions(array $options): void
     {
         $this->slowThreshold = $options['slowThreshold'] ?? 500;
         $this->reportLength = $options['reportLength'] ?? 10;