diff --git a/plugin/src/test/groovy/org/unify4j/String4jTest.java b/plugin/src/test/groovy/org/unify4j/String4jTest.java
new file mode 100644
index 0000000..bb592ca
--- /dev/null
+++ b/plugin/src/test/groovy/org/unify4j/String4jTest.java
@@ -0,0 +1,91 @@
+package org.unify4j;
+
+import org.junit.Test;
+import org.unify4j.common.String4j;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNull;
+
+public class String4jTest {
+
+    @Test
+    public void testStripAccents_NullInput() {
+        assertNull(String4j.stripAccents(null));
+    }
+
+    @Test
+    public void testStripAccents_EmptyString() {
+        assertEquals("", String4j.stripAccents(""));
+    }
+
+    @Test
+    public void testStripAccents_NoAccents() {
+        assertEquals("abcdefg", String4j.stripAccents("abcdefg"));
+    }
+
+    @Test
+    public void testStripAccents_WithAccents() {
+        assertEquals("aeiou", String4j.stripAccents("áéíóú"));
+        assertEquals("aeiou", String4j.stripAccents("àèìòù"));
+        assertEquals("aeiou", String4j.stripAccents("âêîôû"));
+        assertEquals("aeiou", String4j.stripAccents("äëïöü"));
+    }
+
+    @Test
+    public void testStripAccents_MixedCharacters() {
+        assertEquals("Cafe", String4j.stripAccents("Café"));
+        assertEquals("Jose", String4j.stripAccents("José"));
+        assertEquals("Garcon", String4j.stripAccents("Garçon"));
+    }
+
+    @Test
+    public void testStripAccents_ComplexCharacters() {
+        assertEquals("Donna", String4j.stripAccents("Dõñna"));
+        assertEquals("Cu Chulainn", String4j.stripAccents("Cú Chulainn"));
+    }
+
+    @Test
+    public void testUnAccents_EmptyString() {
+        assertEquals("", String4j.unAccents(""));
+    }
+
+    @Test
+    public void testUnAccents_NoNonASCII() {
+        assertEquals("abcdefg", String4j.unAccents("abcdefg"));
+    }
+
+    @Test
+    public void testUnAccents_WithAccents() {
+        assertEquals("aeiou", String4j.unAccents("áéíóú"));
+        assertEquals("aeiou", String4j.unAccents("àèìòù"));
+        assertEquals("aeiou", String4j.unAccents("âêîôû"));
+        assertEquals("aeiou", String4j.unAccents("äëïöü"));
+    }
+
+    @Test
+    public void testUnAccents_MixedCharacters() {
+        assertEquals("Cafe", String4j.unAccents("Café"));
+        assertEquals("Jose", String4j.unAccents("José"));
+        assertEquals("Garcon", String4j.unAccents("Garçon"));
+    }
+
+    @Test
+    public void testUnAccents_ComplexCharacters() {
+        assertEquals("Donna", String4j.unAccents("Dõñna"));
+        assertEquals("Cu Chulainn", String4j.unAccents("Cú Chulainn"));
+    }
+
+    @Test
+    public void testUnAccents_WithNonASCII() {
+        assertEquals("abc123", String4j.unAccents("ábç123"));
+        assertEquals("Hello World", String4j.unAccents("Hëllö Wörld"));
+        assertEquals("ASCIIOnly", String4j.unAccents("ASCIIÖnly"));
+    }
+
+    @Test
+    public void testUnAccents_OnlyNonASCII() {
+        assertEquals("aeioun", String4j.unAccents("áéíóúñ"));
+        assertEquals("oau", String4j.unAccents("öäüß"));
+        assertEquals("cccsz", String4j.unAccents("çćčšž"));
+    }
+}