Dart : Assert statement | Assertions

Assert Statement :

• During development, use an assert statement— assert(<condition>, <optionalMessage>); —to disrupt normal execution if a boolean condition is false.

•   // Make sure the variable has a non-null value.
    assert(text != null);
  
    // Make sure the value is less than 100.
    assert(number < 100);
  
    // Make sure this is an https URL.
    assert(urlString.startsWith('https'));
  

• To attach a message to an assertion, add a string as the second argument to assert (optionally with a trailing comma):

•   assert(urlString.startsWith('https'),
        'URL ($urlString) should start with "https".');
  

• The first argument to assert can be any expression that resolves to a boolean value. If the expression's value is true, the assertion succeeds and execution continues. If it's false, the assertion fails and an exception (an AssertionError) is thrown.