Document assumption that we have a DOMElement object

src/Report/Xml/File.php

@@ -9,6 +9,7 @@
  */
 namespace SebastianBergmann\CodeCoverage\Report\Xml;
 
+use function assert;
 use DOMDocument;
 use DOMElement;
 
@@ -39,6 +40,8 @@ public function totals(): Totals
             );
         }
 
+        assert($totalsContainer instanceof DOMElement);
+
         return new Totals($totalsContainer);
     }
 
@@ -65,6 +68,8 @@ public function lineCoverage(string $line): Coverage
             ),
         );
 
+        assert($lineNode instanceof DOMElement);
+
         return new Coverage($lineNode, $line);
     }
 

src/Report/Xml/Node.php

@@ -9,6 +9,7 @@
  */
 namespace SebastianBergmann\CodeCoverage\Report\Xml;
 
+use function assert;
 use DOMDocument;
 use DOMElement;
 
@@ -43,6 +44,8 @@ public function totals(): Totals
             );
         }
 
+        assert($totalsContainer instanceof DOMElement);
+
         return new Totals($totalsContainer);
     }
 

src/Report/Xml/Project.php

@@ -9,7 +9,9 @@
  */
 namespace SebastianBergmann\CodeCoverage\Report\Xml;
 
+use function assert;
 use DOMDocument;
+use DOMElement;
 
 /**
  * @internal This class is not covered by the backward compatibility promise for phpunit/php-code-coverage
@@ -43,6 +45,8 @@ public function buildInformation(): BuildInformation
             );
         }
 
+        assert($buildNode instanceof DOMElement);
+
         return new BuildInformation($buildNode);
     }
 
@@ -62,6 +66,8 @@ public function tests(): Tests
             );
         }
 
+        assert($testsNode instanceof DOMElement);
+
         return new Tests($testsNode);
     }
 

src/Report/Xml/Report.php

@@ -9,9 +9,11 @@
  */
 namespace SebastianBergmann\CodeCoverage\Report\Xml;
 
+use function assert;
 use function basename;
 use function dirname;
 use DOMDocument;
+use DOMElement;
 
 /**
  * @internal This class is not covered by the backward compatibility promise for phpunit/php-code-coverage
@@ -47,6 +49,8 @@ public function functionObject($name): Method
             ),
         );
 
+        assert($node instanceof DOMElement);
+
         return new Method($node, $name);
     }
 
@@ -76,6 +80,8 @@ public function source(): Source
             );
         }
 
+        assert($source instanceof DOMElement);
+
         return new Source($source);
     }
 
@@ -94,6 +100,8 @@ private function unitObject(string $tagName, $name): Unit
             ),
         );
 
+        assert($node instanceof DOMElement);
+
         return new Unit($node, $name);
     }
 }

src/Report/Xml/Unit.php

@@ -68,6 +68,8 @@ public function addMethod(string $name): Method
             ),
         );
 
+        assert($node instanceof DOMElement);
+
         return new Method($node, $name);
     }