### Question:
Calculator { public double add(double left, double right) { addToHistory(left, '+', right); return left + right; }  static Calculator getInstance(); double add(double left, double right); double subtract(double left, double right); double multiply(double left, double right); double divide(double left, double right); List<Operation> getOperations();  }### Answer:
@Test public void testAddition() throws Exception { assertEquals(3.0d, new Calculator().add(1.0d, 2.0d), 0.0000001d); }