Previously, Watch did not validate the "fullDocument" option and neglected to pass "readConcern" and "readPreference" to Aggregate. This refactors the class so that Watch only processes its own options.

Additionally, Aggregate is now first created from Watch::__construct() instead of Watch::execute(), which allows its options to be validated earlier (akin to FindOne creating Find in its constructor). Aggregate is only recreated if a new resume token is provided during a resume.

Read concern is supported by all server versions that support change streams, so we need not discuss its requirement.

The spec requests that we check that the initial change stream cursor is alive. This can be done by both asserting its cursor ID is non-zero and also calling MongoDB\Driver\Cursor::isDead().

Previously, iteration started with next(), so the first element's key was 1. Iteration should being with rewind() and the initial key should be zero.

With this change, we're still testing that the key is only incremented when next() successfully increments.

Resume tests for rewind() will be reimplemented in PHPLIB-322

This also adds more assertions between the doc examples.

This also removes the hard-coded database and collection names, which are subject to change based on the test suite configuration and getCollectionName() implementation.

The original intention of this test was to verify resumability in the event of a dropped connection; however, since socketTimeoutMS and maxAwaitTimeMS are fixed values, we cannot test a dropped connection followed by a successful resume. Instead, we will test that the driver attempts to resume once and only once before we expect a socket timeout after the second attempt.

Note: ChangeStream::rewind() does not currently resume (see: PHPLIB-322)

Change streams require a replica set.

Refactoring the change stream tests to execute Watch directly highlighted a bug where no read preference was available during the resume process. This ensures that a read preference is always set, and also specifies a "fullDocument" default (consistent with other drivers).

For consistency with other operation functional tests, this now constructs and executes operation classes directly.

The batchSize option for change streams is not identical to the aggregate option, so they should not share the same text. That said, the batchSize option likely has no effect on the resulting change stream (see: PHPLIB-321).

This makes the constructor consistent with other classes (e.g. Client, GridFS\Bucket) and also ensures that we don't have required parameters trailing optional arguments (i.e. options array).

This makes the operation consistent with the Collection method name and avoids the naming conflict with the ChangeStream iterator class.