diff --git a/.github/workflows/integration.yml b/.github/workflows/integration.yml
index 075e0bd..77f8a41 100644
--- a/.github/workflows/integration.yml
+++ b/.github/workflows/integration.yml
@@ -45,8 +45,8 @@ jobs:
         run: |
           composer install --no-progress --prefer-dist --optimize-autoloader
 
-      #- name: Run Tests
-      #  run: php vendor/bin/phpunit --coverage-text
+      - name: Run Tests
+        run: php vendor/bin/phpunit --coverage-text
 
   coding-standard:
     name: Coding Standard
diff --git a/src/NodeVisitor/ClassConstant.php b/src/NodeVisitor/ClassConstant.php
index 7e5ca6d..8ea8f58 100644
--- a/src/NodeVisitor/ClassConstant.php
+++ b/src/NodeVisitor/ClassConstant.php
@@ -10,9 +10,11 @@
 
 namespace OpenCodeModeling\CodeAst\NodeVisitor;
 
+use OpenCodeModeling\CodeAst\Code\ClassConstGenerator;
 use OpenCodeModeling\CodeAst\Code\IdentifierGenerator;
 use PhpParser\Node;
 use PhpParser\Node\Stmt\Class_;
+use PhpParser\Node\Stmt\Namespace_;
 use PhpParser\NodeVisitorAbstract;
 
 final class ClassConstant extends NodeVisitorAbstract
@@ -27,53 +29,62 @@ public function __construct(IdentifierGenerator $lineGenerator)
         $this->lineGenerator = $lineGenerator;
     }
 
-    public function enterNode(Node $node)
+    public static function forClassConstant(
+        string $constantName,
+        string $constantValue,
+        int $flags = ClassConstGenerator::FLAG_PUBLIC
+    ): ClassConstant {
+        return new self(
+            new IdentifierGenerator(
+                $constantName,
+                new ClassConstGenerator($constantName, $constantValue, $flags)
+            )
+        );
+    }
+
+    public function afterTraverse(array $nodes): ?array
     {
-        if ($node instanceof Class_) {
-            if ($definitions = $this->constant($node)) {
+        $newNodes = [];
+
+        foreach ($nodes as $node) {
+            $newNodes[] = $node;
+
+            if ($node instanceof Namespace_) {
+                foreach ($node->stmts as $stmt) {
+                    if ($stmt instanceof Class_) {
+                        if ($this->checkConstantExists($stmt)) {
+                            return null;
+                        }
+                        $stmt->stmts = \array_merge(
+                            $this->lineGenerator->generate(),
+                            $stmt->stmts
+                        );
+                    }
+                }
+            } elseif ($node instanceof Class_) {
+                if ($this->checkConstantExists($node)) {
+                    return null;
+                }
                 $node->stmts = \array_merge(
-                    $definitions,
+                    $this->lineGenerator->generate(),
                     $node->stmts
                 );
-
-                return $node;
             }
         }
 
-        return null;
+        return $newNodes;
     }
 
-    private function isAlreadyDefined(
-        string $lineIdentifier,
-        Class_ $node
-    ): bool {
-        $alreadyDefined = false;
-
+    private function checkConstantExists(Class_ $node): bool
+    {
         foreach ($node->stmts as $stmt) {
-            if (! $stmt instanceof Node\Stmt\ClassConst) {
-                continue;
-            }
-
-            if ($lineIdentifier === $stmt->consts[0]->name->name) {
-                $alreadyDefined = true;
-                break;
+            if ($stmt instanceof Node\Stmt\ClassConst
+                && $stmt->consts[0]->name->name === $this->lineGenerator->getIdentifier()
+            ) {
+                return true;
             }
         }
 
-        return $alreadyDefined;
-    }
-
-    private function constant(Class_ $node): ?array
-    {
-        $isAlreadyDefined = $this->isAlreadyDefined(
-            $this->lineGenerator->getIdentifier(),
-            $node
-        );
-
-        if ($isAlreadyDefined === false) {
-            return $this->lineGenerator->generate();
-        }
-
-        return null;
+        return false;
     }
 }
diff --git a/tests/NodeVisitor/ClassConstantTest.php b/tests/NodeVisitor/ClassConstantTest.php
new file mode 100644
index 0000000..992285e
--- /dev/null
+++ b/tests/NodeVisitor/ClassConstantTest.php
@@ -0,0 +1,144 @@
+<?php
+
+declare(strict_types=1);
+
+namespace OpenCodeModelingTest\CodeAst\NodeVisitor;
+
+use OpenCodeModeling\CodeAst\Code\ClassConstGenerator;
+use OpenCodeModeling\CodeAst\Code\ClassGenerator;
+use OpenCodeModeling\CodeAst\NodeVisitor\ClassConstant;
+use OpenCodeModeling\CodeAst\NodeVisitor\ClassFile;
+use OpenCodeModeling\CodeAst\NodeVisitor\ClassNamespace;
+use OpenCodeModeling\CodeAst\NodeVisitor\StrictType;
+use OpenCodeModeling\JsonSchemaToPhpAst\ValueObject\BooleanFactory;
+use PhpParser\NodeTraverser;
+use PhpParser\Parser;
+use PhpParser\ParserFactory;
+use PhpParser\PrettyPrinter\Standard;
+use PHPUnit\Framework\TestCase;
+
+final class ClassConstantTest extends TestCase
+{
+    /**
+     * @var Parser
+     */
+    private $parser;
+
+    /**
+     * @var Standard
+     */
+    private $printer;
+
+    public function setUp(): void
+    {
+        $this->parser = (new ParserFactory())->create(ParserFactory::ONLY_PHP7);
+        $this->printer = new Standard(['shortArraySyntax' => true]);
+    }
+
+    /**
+     * @test
+     */
+    public function it_generates_constant_for_class_for_empty_file(): void
+    {
+        $ast = $this->parser->parse('');
+
+        $nodeTraverser = new NodeTraverser();
+        $nodeTraverser->addVisitor(new StrictType());
+        $nodeTraverser->addVisitor(new ClassFile(new ClassGenerator('TestClass')));
+        $nodeTraverser->addVisitor(ClassConstant::forClassConstant('TYPE_STRING', 'string'));
+
+        $expected = <<<'EOF'
+<?php
+
+declare (strict_types=1);
+class TestClass
+{
+    public const TYPE_STRING = 'string';
+}
+EOF;
+
+        $this->assertSame($expected, $this->printer->prettyPrintFile($nodeTraverser->traverse($ast)));
+    }
+
+    /**
+     * @test
+     */
+    public function it_generates_constant_for_class_for_existing_file(): void
+    {
+        $ast = $this->parser->parse('<?php class TestClass {}');
+
+        $nodeTraverser = new NodeTraverser();
+        $nodeTraverser->addVisitor(ClassConstant::forClassConstant('TYPE_STRING', 'string', ClassConstGenerator::FLAG_PRIVATE));
+
+        $expected = <<<'EOF'
+<?php
+
+class TestClass
+{
+    private const TYPE_STRING = 'string';
+}
+EOF;
+
+        $this->assertSame($expected, $this->printer->prettyPrintFile($nodeTraverser->traverse($ast)));
+    }
+
+    /**
+     * @test
+     */
+    public function it_generates_constant_for_class_with_namespace_for_empty_file(): void
+    {
+        $ast = $this->parser->parse('');
+
+        $nodeTraverser = new NodeTraverser();
+        $nodeTraverser->addVisitor(new StrictType());
+        $nodeTraverser->addVisitor(new ClassNamespace('My\\Awesome\\Service'));
+        $nodeTraverser->addVisitor(new ClassFile(new ClassGenerator('TestClass')));
+        $nodeTraverser->addVisitor(ClassConstant::forClassConstant('TYPE_STRING', 'string'));
+
+        $expected = <<<'EOF'
+<?php
+
+declare (strict_types=1);
+namespace My\Awesome\Service;
+
+class TestClass
+{
+    public const TYPE_STRING = 'string';
+}
+EOF;
+
+        $this->assertSame($expected, $this->printer->prettyPrintFile($nodeTraverser->traverse($ast)));
+    }
+
+    /**
+     * @test
+     */
+    public function it_generates_constant_for_class_with_namespace_for_existing_file(): void
+    {
+        $code = <<<'PHP'
+<?php
+
+namespace My\Awesome\Service;
+
+class TestClass {}
+PHP;
+
+        $ast = $this->parser->parse($code);
+
+        $nodeTraverser = new NodeTraverser();
+        $nodeTraverser->addVisitor(ClassConstant::forClassConstant('TYPE_STRING', 'string', ClassConstGenerator::FLAG_PRIVATE));
+
+        $expected = <<<'EOF'
+<?php
+
+namespace My\Awesome\Service;
+
+class TestClass
+{
+    private const TYPE_STRING = 'string';
+}
+EOF;
+
+        $this->assertSame($expected, $this->printer->prettyPrintFile($nodeTraverser->traverse($ast)));
+    }
+}