Fix type errors in PhptTestCase

Author: staabm

src/Runner/PHPT/PhptTestCase.php

@@ -561,7 +561,9 @@ private function parseExternal(array &$sections): void
                     );
                 }
 
-                $sections[$section] = file_get_contents($testDirectory . $externalFilename);
+                $contents = file_get_contents($testDirectory . $externalFilename);
+                assert($contents !== false && $contents !== '');
+                $sections[$section] = $contents;
             }
         }
     }
@@ -694,9 +696,9 @@ private function renderForCoverage(string &$job, bool $pathCoverage, ?string $co
 
         file_put_contents($files['job'], $job);
 
-        $job = $template->render();
-
-        assert($job !== '');
+        $rendered = $template->render();
+        assert($rendered !== '');
+        $job = $rendered;
     }
 
     private function cleanupForCoverage(): RawCodeCoverageData