diff --git a/AlgebraicDataflowArchitectureModel/src/tests/NumberUtilTest.java b/AlgebraicDataflowArchitectureModel/src/tests/NumberUtilTest.java
new file mode 100644
index 0000000..31c7f7e
--- /dev/null
+++ b/AlgebraicDataflowArchitectureModel/src/tests/NumberUtilTest.java
@@ -0,0 +1,48 @@
+package tests;
+
+import code.ast.NumberUtil;
+import org.junit.Test;
+
+import static org.junit.Assert.assertFalse;
+import static org.junit.Assert.assertTrue;
+
+public class NumberUtilTest {
+	@Test
+	public void testIsHexNumber() {
+		// --- Valid format numbers ---
+		assertTrue("Standard hex", NumberUtil.isHexNumber("0x123456789ABCDEF"));
+		assertTrue("Mixed case prefix", NumberUtil.isHexNumber("0Xabcdef"));
+		assertTrue("Hex with underscores", NumberUtil.isHexNumber("0x123_456"));
+		assertTrue("Hex with long suffix (L)", NumberUtil.isHexNumber("0x123L"));
+		assertTrue("Hex with long suffix (l)", NumberUtil.isHexNumber("0x123l"));
+		assertTrue("Minimum valid hex", NumberUtil.isHexNumber("0x0"));
+
+		// --- Invalid format numbers ---
+		// Null and empty
+		assertFalse("Null string", NumberUtil.isHexNumber(null));
+		assertFalse("Empty string", NumberUtil.isHexNumber(""));
+		assertFalse("Prefix only", NumberUtil.isHexNumber("0x"));
+
+		// Incorrect prefix
+		assertFalse("Missing prefix", NumberUtil.isHexNumber("123"));
+		assertFalse("Invalid prefix (0y)", NumberUtil.isHexNumber("0y123"));
+		assertFalse("Leading space", NumberUtil.isHexNumber(" 0x123"));
+
+		// Invalid characters
+		assertFalse("Invalid character (g)", NumberUtil.isHexNumber("0x12g"));
+		assertFalse("Decimal point", NumberUtil.isHexNumber("0x1.2"));
+
+		// Underscore placement rules
+		assertFalse("Underscore immediately after prefix", NumberUtil.isHexNumber("0x_123"));
+		assertFalse("Trailing underscore", NumberUtil.isHexNumber("0x123_"));
+		assertFalse("Trailing underscore with L", NumberUtil.isHexNumber("0x123_L"));
+
+		// Long suffix rules
+		assertFalse("L in middle", NumberUtil.isHexNumber("0x1L2"));
+		assertFalse("Multiple L", NumberUtil.isHexNumber("0x1LL"));
+		assertFalse("L with invalid char", NumberUtil.isHexNumber("0x1GL"));
+
+		// No digits
+		assertFalse("No hex digits (0xL)", NumberUtil.isHexNumber("0xL"));
+	}
+}