Non-nullable property 'Name' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Non-nullable property 'Player' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Non-nullable property 'Achievement' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Non-nullable property 'Name' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Non-nullable property 'Achievements' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

Non-nullable property 'Name' must contain a non-null value when exiting constructor. Consider adding the 'required' modifier or declaring the property as nullable.

The literal or constant value 1 should be passed as the 'expected' argument in the call to 'Assert.Equal(expected, actual)' in method 'PostAnotherAchievement' on type 'AchievementServiceTests'. Swap the parameter values. (https://xunit.net/xunit.analyzers/rules/xUnit2000)

The literal or constant value 2 should be passed as the 'expected' argument in the call to 'Assert.Equal(expected, actual)' in method 'PostAnotherAchievement' on type 'AchievementServiceTests'. Swap the parameter values. (https://xunit.net/xunit.analyzers/rules/xUnit2000)

Do not use Assert.Equal() to check for collection size. Use Assert.Single instead. (https://xunit.net/xunit.analyzers/rules/xUnit2013)