Have

ShouldHaveCount

var maggie = new Person { Name = "Maggie" };
var homer = new Person { Name = "Homer" };
var simpsonsBabies = new List<Person> { homer, maggie };
simpsonsBabies.ShouldHaveCount(3);

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Exception

simpsonsBabies
    should have 3 items but had
2
    items and was
[Homer, Maggie]

ShouldHaveSingleItem

var maggie = new Person { Name = "Maggie" };
var homer = new Person { Name = "Homer" };
var simpsonsBabies = new List<Person> { homer, maggie };
simpsonsBabies.ShouldHaveSingleItem();

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Exception

simpsonsBabies
    should have single item but had
2
    items and was
[Homer, Maggie]