anchor.diff:      }
     }
   
  +  @override
  +  visitCompilationUnit(CompilationUnit node) {
  +    boolType = node.element.context.typeProvider.boolType;
  +  }
  +
     DartType _unbound(DartType type) {
       DartType t = type;
       while (t is TypeParameterType) t = (t as TypeParameterType).bound;
  
positive.code: }
  
  class Visitor extends SimpleAstVisitor {
    Visitor(this.rule);
  
    final LintRule rule;
    DartType boolType;
  
    @override
    visitCompilationUnit(CompilationUnit node) {
      boolType = node.element.context.typeProvider.boolType;
    }
  
    @override
    visitAssertStatement(AssertStatement node) {
  
negative.code: import 'package:analyzer/dart/ast/visitor.dart';
  import 'package:analyzer/dart/element/type.dart';
  import 'package:linter/src/analyzer.dart';
  
  const _desc = r'Prefer using a boolean as the assert condition.';
  
  