test: add mroot InvalidNumberOfChildrenError case

__test__/index.test.ts

@@ -340,6 +340,7 @@ describe('#convert', () => {
         const mathml = mathmlStrings.shortMFrac;
 
         const result = MathMLToLaTeX.convert(mathml);
+
         expect(result).toMatch('1/\\left(x^{3} + 3\\right)');
       });
     });
@@ -349,20 +350,34 @@ describe('#convert', () => {
         const mathml = mathmlStrings.mfracWithThreeChildren;
 
         const result = () => MathMLToLaTeX.convert(mathml);
+
         expect(result).toThrow(new InvalidNumberOfChildrenError('mfrac', 2, 3));
       });
     });
   });
 
-  describe('given math string with mroot containing two content', () => {
+  describe('given math string with mroot', () => {
+    describe('containing two content', () => {
       it('convert mroot tag wrapping its contents inside \\sqrt command and root parameter', () => {
         const mathml = mathmlStrings.mroot;
 
         const result = MathMLToLaTeX.convert(mathml);
+
         expect(result).toMatch('\\sqrt[3]{x + 2}');
       });
     });
 
+    describe('containing three children', () => {
+      it('throw InvalidNumberOfChildrenError', () => {
+        const mathml = mathmlStrings.mrootWithThreeChildren;
+
+        const result = () => MathMLToLaTeX.convert(mathml);
+
+        expect(result).toThrow(new InvalidNumberOfChildrenError('mroot', 2, 3));
+      });
+    });
+  });
+
   describe('given math string with mpadded tag', () => {
     it('convert mpadded just wrapping its content', () => {
       const mathml = mathmlStrings.mpadded;

__test__/mocks/mathmlStrings.ts

@@ -710,6 +710,22 @@ export const mroot = `
 </root>
 `;
 
+export const mrootWithThreeChildren = `
+<root>
+  <math>
+    <mroot>
+      <mrow>
+        <mi>x</mi>
+        <mo>+</mo>
+        <mi>2</mi>
+      </mrow>
+      <mn>3</mn>
+      <mn>2</mn>
+    </mroot> 
+  </math>
+</root>
+`;
+
 export const mpadded = `
 <root>
   <math>