"Fixed" test class

src/main/java/resources/CalculatorResource.java

@@ -21,7 +21,7 @@ public class CalculatorResource {
     @POST
     @Consumes(MediaType.TEXT_PLAIN)
     @Produces(MediaType.TEXT_PLAIN)
-    public double calculate(String expression){
+    public String calculate(String expression){
         // Removes all whitespaces
         String expressionTrimmed = expression.replaceAll("\\s+","");
 
@@ -46,9 +46,10 @@ public class CalculatorResource {
             result = multiplication(expressionTrimmed);
         } else if(expressionTrimmed.matches("^\\d+(?:\\s*[/]\\s*\\d+)*$")) {
             result = division(expressionTrimmed);
+        } else {
+            return "error";
         }
-
-        return result;
+        return String.valueOf(result);
     }
 
     /**

src/test/java/CalculatorResourceTest.java

@@ -11,16 +11,16 @@ public class CalculatorResourceTest{
         CalculatorResource calculatorResource = new CalculatorResource();
 
         String expression = "100+300";
-        assertEquals(400, calculatorResource.calculate(expression));
+        assertEquals("400.0", calculatorResource.calculate(expression));
 
         expression = " 300 - 99 ";
-        assertEquals(201, calculatorResource.calculate(expression));
+        assertEquals("201.0", calculatorResource.calculate(expression));
 
         expression = "5*2";
-        assertEquals(10, calculatorResource.calculate(expression));
+        assertEquals("10.0", calculatorResource.calculate(expression));
 
         expression = "5/2";
-        assertEquals(2.5, calculatorResource.calculate(expression));
+        assertEquals("2.5", calculatorResource.calculate(expression));
     }
 
     @Test