checkSnapshotValid(snapshot, callback) {
		const cachedResult = this._snapshotCache.get(snapshot);
		if (cachedResult !== undefined) {
			this._statTestedSnapshotsCached++;
			if (typeof cachedResult === "boolean") {
				callback(null, cachedResult);
			} else {
				cachedResult.push(callback);
			}
			return;
		}
		this._statTestedSnapshotsNotCached++;
		this._checkSnapshotValidNoCache(snapshot, callback);
	}
@param {Snapshot} snapshot the snapshot made
@param {CheckSnapshotValidCallback} callback callback function
@returns {void}