Fix #5481: add modules should work for Builder beyond build() method

Author: cowtowncoder

src/test/java/tools/jackson/databind/module/BuilderModuleReuse5481Test.java

@@ -0,0 +1,79 @@
+package tools.jackson.databind.module;
+
+import java.util.*;
+
+import org.junit.jupiter.api.Test;
+
+import tools.jackson.core.Version;
+import tools.jackson.databind.*;
+import tools.jackson.databind.json.JsonMapper;
+import tools.jackson.databind.testutil.DatabindTestUtil;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+/**
+ * Test for [databind#5481]: JsonMapper.Builder module registration bug
+ * when reusing builder instance between multiple builds with different modules.
+ */
+@SuppressWarnings("serial")
+public class BuilderModuleReuse5481Test extends DatabindTestUtil
+{
+    // Test modules with distinct names for easy identification
+    static class ModuleA extends SimpleModule {
+        public ModuleA() {
+            super("ModuleA", Version.unknownVersion());
+        }
+    }
+
+    static class ModuleB extends SimpleModule {
+        public ModuleB() {
+            super("ModuleB", Version.unknownVersion());
+        }
+    }
+
+    static class ModuleC extends SimpleModule {
+        public ModuleC() {
+            super("ModuleC", Version.unknownVersion());
+        }
+    }
+
+    /**
+     * Test case demonstrating issue #5481: when reusing a JsonMapper.Builder,
+     * calling modules() multiple times between builds should reflect in each
+     * new mapper instance, but currently only the first set of modules is
+     * registered in all instances.
+     */
+    @Test
+    public void testBuilderReuseWithDifferentModules() {
+        ModuleA moduleA = new ModuleA();
+        ModuleB moduleB = new ModuleB();
+        ModuleC moduleC = new ModuleC();
+
+        // Create a builder and register first set of modules
+        JsonMapper.Builder builder = JsonMapper.builder()
+                .addModule(moduleA)
+                .addModule(moduleB);
+
+        // Build first mapper
+        ObjectMapper mapper1 = builder.build();
+
+        // Verify first mapper has modules A, B
+        Collection<JacksonModule> modules1 = mapper1.registeredModules();
+        assertEquals(List.of("ModuleA", "ModuleB"), getModuleNames(modules1));
+
+        // Now reuse the builder and register different modules
+        builder.addModule(moduleC);
+
+        // Build second mapper
+        ObjectMapper mapper2 = builder.build();
+
+        // BUG: Second mapper should have modules A, B, C
+        // but according to issue #5481, it incorrectly only has A, B
+        Collection<JacksonModule> modules2 = mapper2.registeredModules();
+        assertEquals(List.of("ModuleA", "ModuleB", "ModuleC"), getModuleNames(modules2));
+    }
+
+    private List<String> getModuleNames(Collection<JacksonModule> modules) {
+        return modules.stream().map(JacksonModule::getModuleName).toList();
+    }
+}