test: add munderover error test case

__test__/index.test.ts

@@ -1,5 +1,6 @@
 import MathMLToLaTeX from '../src';
 import * as mathmlStrings from './mocks/mathmlStrings';
+import { InvalidNumberOfChild } from '../src/data/errors/InvalidNumberOfChild';
 
 describe('#convert', () => {
   describe('given math string with mi tag', () => {
@@ -883,6 +884,16 @@ describe('#convert', () => {
         expect(result).toBe('\\int_{0}^{\\infty}');
       });
     });
+
+    describe('with munderover with 4 children', () => {
+      it('should throws InvalidNumberOfChildErrors', () => {
+        const mathml = mathmlStrings.munderoverWithThreeChildren;
+
+        const result = () => MathMLToLaTeX.convert(mathml);
+
+        expect(result).toThrow(new InvalidNumberOfChild('munderover', 3, 4));
+      });
+    });
   });
 
   describe('given math string with mmultiscript', () => {

__test__/mocks/mathmlStrings.ts

@@ -1472,6 +1472,19 @@ export const munderoverEncoded = `
 </root>
 `;
 
+export const munderoverWithThreeChildren = `
+<root>
+  <math>
+    <munderover>
+      <mo> &#x222B;</mo>
+      <mn> 0 </mn>
+      <mi> &#x221E; </mi>
+      <mi> 1 </mi>
+    </munderover>
+  </math>
+</root>
+`;
+
 export const mmultiscript = `<math xmlns="http://www.w3.org/1998/Math/MathML" display="block">
 <mmultiscripts>
   <mrow>