public void should_return_casted_result_if_it_is_castable()
{
var demoClass = new PolymorphismDemoClass();
var castToBaseClass = demoClass as PolymorphismDemoClassBase;
bool isNull = castToBaseClass == null;
// please change the variable value to fix the test.
const bool expected = false;
Assert.Equal(expected, isNull);
}
public void should_reference_to_same_object_after_casting()
{
var demoClass = new PolymorphismDemoClass();
var castToBaseClass = (PolymorphismDemoClassBase)demoClass;
bool referenceEqual = ReferenceEquals(demoClass, castToBaseClass);
// please change the variable value to fix the test.
const bool expected = true;
Assert.Equal(expected, referenceEqual);
}
[Fact] /////public修饰的子类强转成父类，调用时是自己的方法；
public void should_access_member_of_most_derived_class()
{
var demoClass = new PolymorphismDemoClass();
var castToBaseClass = (PolymorphismDemoClassBase)demoClass;
string actualValue = castToBaseClass.VirtualMethod();
// please change the variable value to fix the test.
const string expected = "DerivedClass";
Assert.Equal(expected, actualValue);
}
public void should_throw_exception_if_it_is_not_castable()
{
var demoClass = new PolymorphismDemoClass();
object castToObject = demoClass;
// please change the variable value to fix the test.
Type expectedExceptionType = typeof(InvalidCastException);
Assert.NotEqual(typeof(SystemException), expectedExceptionType);
Assert.NotEqual(typeof(Exception), expectedExceptionType);
Assert.Throws(expectedExceptionType, () => (StringBuilder)castToObject);
}
public void should_return_null_if_it_is_not_castable()
{
var demoClass = new PolymorphismDemoClass();
object castToObject = demoClass;
var castResult = castToObject as StringBuilder;
bool isNull = castResult == null;
// please change the variable value to fix the test.
const bool expected = true;
Assert.Equal(expected, isNull);
}
public void should_return_casted_result_if_it_is_castable()
{
var demoClass = new PolymorphismDemoClass();
var castToBaseClass = demoClass as PolymorphismDemoClassBase;
bool isNull = castToBaseClass == null;
// please change the variable value to fix the test.
// as works similar with cast, but it will never throw an exception and it only returns null
const bool expected = false;
Assert.Equal(expected, isNull);
}
public void should_return_null_if_it_is_not_castable()
{
// normaly (super_class)class is castable, as keyword
var demoClass = new PolymorphismDemoClass();
object castToObject = demoClass;
// StringBuilder and object are not in a inheritance chain ?, so caseResult is null
var castResult = castToObject as StringBuilder;
bool isNull = castResult == null;
// please change the variable value to fix the test.
const bool expected = true;
Assert.Equal(expected, isNull);
}
public void should_access_member_of_most_derived_class()
{
// virtual method use override to override, difference with abstract method?
// in super class declare method can be override use virtual
// in sub class declare method with override
var demoClass = new PolymorphismDemoClass();
var castToBaseClass = (PolymorphismDemoClassBase)demoClass;
string actualValue = castToBaseClass.VirtualMethod();
// please change the variable value to fix the test.
const string expected = "DerivedClass";
Assert.Equal(expected, actualValue);
}
public void should_return_casted_result_if_it_is_castable()
{
// force convert (cast) doesn't change the type of object, only treat object as it's converted type
// PolymorphismDemoClass and -Base are in the same inheritance chain
var demoClass = new PolymorphismDemoClass();
// var baseDemo = new PolymorphismDemoClassBase();
// Assert.Equal(demoClass, baseDemo); not equal
// as returns null instead of raising exception when casing is impossible
var castToBaseClass = demoClass as PolymorphismDemoClassBase;
bool isNull = castToBaseClass == null;
// please change the variable value to fix the test.
const bool expected = false;
Assert.Equal(expected, isNull);
// Assert.Equal(demoClass.GetType(), (new PolymorphismDemoClass()).GetType());
// Assert.Equal(castToBaseClass, baseDemo);
// Assert.Equal(demoClass, baseDemo); not equal
// Assert.Equal(demoClass, castToBaseClass); equal
// Assert.Equal(baseDemo, castToBaseClass); not equal
}