--fix : code coverage 100%

Author: TheSTL

src/_DataStructures_/Stack/postfix-expression-evaluation/index.js

@@ -43,7 +43,7 @@ function evaluatePostfixExpression(expression) {
           s.push(val2 / val1);
           break;
         default:
-          break;
+          throw new Error('Operation is not valid');
       }
     }
   }

src/_DataStructures_/Stack/postfix-expression-evaluation/postfix-expression-evaluation.test.js

@@ -58,5 +58,8 @@ describe('Postfix expression evaluation', () => {
     test.each(invalidExpressions)('running for %p', (expression) => {
       expect(() => evaluatePostfixExpression(expression)).toThrow(ERROR_STRING);
     });
+
+    expect(() => evaluatePostfixExpression('1&2')).toThrow('Operation is not valid');
+
   });
 });