add test return types

Author: jrushlow

src/Test/MakerTestProcess.php

@@ -54,17 +54,17 @@ public function run($allowToFail = false, array $envVars = []): self
         return $this;
     }
 
-    public function isSuccessful()
+    public function isSuccessful(): bool
     {
         return $this->process->isSuccessful();
     }
 
-    public function getOutput()
+    public function getOutput(): string
     {
         return $this->process->getOutput();
     }
 
-    public function getErrorOutput()
+    public function getErrorOutput(): string
     {
         return $this->process->getErrorOutput();
     }