Hamcrest 的 hasItems，包含和包含 InAnyOrder 有什么不同？

Hamcrest 为断言集合的内容提供了许多匹配器:

Collection<String> c = ImmutableList.of("one", "two", "three");
assertThat(c, hasItems("one", "two", "three");
assertThat(c, contains("one", "two", "three");
assertThat(c, containsInAnyOrder("one", "two", "three");

hasItems、 contains和 containsInAnyOrder有什么不同？

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hasItems checks:

consecutive passes over the examined Iterable yield at least one item that is equal to the corresponding item from the specified items.

That is, it makes sure that the collections contains at least these items, in any order. So,

assertThat(c, hasItems("one", "two"));

would also pass, with the extra item being ignored. And:

assertThat(c, hasItems("three", "two", "one"));

would also pass.

contains checks:

a single pass over the examined Iterable yields a series of items, each logically equal to the corresponding item in the specified items. For a positive match, the examined iterable must be of the same length as the number of specified items.

So it makes sure that the collection contains exactly these items:

assertThat(c, contains("one", "two")); // Fails

This would fail, as the leftover "three" is not matched.

assertThat(c, contains("three", "two", "one")); // Fails

This fails because the corresponding items don't match.

Another related matcher, containsInAnyOrder, checks that exactly those items are present, but in any order:

Creates an order agnostic matcher for Iterables that matches when a single pass over the examined Iterable yields a series of items, each logically equal to one item anywhere in the specified items.

A test with a missing item fails:

assertThat(c, containsInAnyOrder("one", "two")); // Fails

But all items in a different order will pass:

assertThat(c, containsInAnyOrder("three", "two", "one"));

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