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Statistics

MockFileSystem.Statistics records every call made through the mock: which property was accessed, which method was invoked, with what arguments. Use it to assert what a system under test did, not just what it produced.

MockFileSystem fileSystem = new();

fileSystem.File.WriteAllText("catalog.json", "[]");
fileSystem.File.ReadAllText("catalog.json");

IFileSystemStatistics stats = fileSystem.Statistics;
await That(stats.TotalCount).IsEqualTo(2);
await That(stats.File.Methods).Contains(m => m.Name == nameof(IFile.WriteAllText));

What is recorded​

IFileSystemStatistics exposes one property per IFileSystem sub-property (Directory, DirectoryInfo, DriveInfo, File, FileInfo, FileStream, FileSystemWatcher, FileVersionInfo, Path and RandomAccess).

Each of them has Methods and Properties collections. An entry carries the call's name, its parameters and a global Counter that tells the order of the calls.

The properties for types created by a factory (DirectoryInfo, DriveInfo, FileInfo, FileStream, FileSystemWatcher, FileVersionInfo) also have an indexer keyed by path: stats.FileInfo["catalog.json"] returns just the calls made on the IFileInfo for that path:

_ = fileSystem.FileInfo.New("catalog.json").Exists;

await That(stats.FileInfo["catalog.json"].Properties)
    .Contains(p => p.Name == nameof(IFileInfo.Exists));

TotalCount returns the sum across every sub-property, which is handy for "did anything touch the file system at all?" assertions.

What is not recorded​

Calls inside the testing helpers themselves (Initialize, InitializeFromRealDirectory, SetCurrentDirectoryToEmptyTemporaryDirectory, …) are excluded from the statistics so seeding does not pollute your assertions.