ReplayFileSystem class

A file system that replays invocations from a prior recording for use in tests.

This will replay all invocations (methods, property getters, and property setters) that occur on it, based on an opaque recording that was generated in RecordingFileSystem. All activity in the File, Directory, Link, IOSink, and RandomAccessFile instances returned from this API will also be replayed from the same recording.

Once an invocation has been replayed once, it is marked as such and will not be eligible for further replay. If an eligible invocation cannot be found that matches an incoming invocation, a NoMatchingInvocationError will be thrown.

This class is intended for use in tests, where you would otherwise have to set up complex mocks or fake file systems. With this class, the process is as follows:

• You record the file system activity during a real run of your program by injecting a RecordingFileSystem that delegates to your real file system.
• You serialize that recording to disk as your program finishes.
• You use that recording in tests to create a mock file system that knows how to respond to the exact invocations your program makes. Any invocations that aren't in the recording will throw, and you can make assertions in your tests about which methods were invoked and in what order.

Implementation note: this class uses noSuchMethod to dynamically handle invocations. As a result, method references on objects herein will not pass is checks or checked-mode checks on type. For example:

typedef FileStat StatSync(String path);
FileSystem fs = new ReplayFileSystem(directory);

StatSync method = fs.statSync;     // Will fail in checked-mode
fs.statSync is StatSync            // Will return false
fs.statSync is Function            // Will return false

dynamic method2 = fs.statSync;     // OK
FileStat stat = method2('/path');  // OK

See also:

• RecordingFileSystem