void visit(ASTNode[] nodes, SourceUnit source) {
        def clazz = (ClassNode) nodes[1]
        clazz.addField("magicField", Modifier.PUBLIC, ClassHelper.STRING_TYPE, new ConstantExpression("magicValue"))
    }

import org.junit.Test

@GroovyMagicField
class GroovyMagicFieldTransformTest {
    @Test
    void transformHasBeenApplied() {
        assert getClass().declaredFields.find { it.name == "magicField" }
        assert magicField == "magicValue"
    }

@MagicField @MagicInterface
class MagicFieldTransformTest {
    @Test
    void transformHasBeenApplied() {
        assert getClass().declaredFields.find { it.name == "magicField" }
        assert magicField == "magicValue"
        assert this instanceof Marker
    }

import org.junit.Test

@GroovyMagicField
class GroovyMagicFieldTransformTest {
    @Test
    void transformHasBeenApplied() {
        assert getClass().declaredFields.find { it.name == "magicField" }
        assert magicField == "magicValue"
    }

    public void visit(ASTNode[] nodes, SourceUnit source) {
        ClassNode clazz = (ClassNode) nodes[1];
        clazz.addField("magicField", Modifier.PUBLIC, ClassHelper.STRING_TYPE, new ConstantExpression("magicValue"));
    }

        StringExpressionThroughAsm() {
            super(ClassHelper.STRING_TYPE)
        }

        @Override
        void visit(MethodVisitor methodVisitor) {
            methodVisitor.visitLdcInsn("magicValue")
        }
    }