Helper methods

A helper method can call InlineSnapshot.Validate to share settings or preparation between tests. The snapshot to update is then an argument of the call to the helper, not of the call to Validate. Tell the library where it is:

1. Decorate the helper with [InlineSnapshotAssertion], and give it the name of the parameter that holds the snapshot.
2. Add [CallerFilePath] and [CallerLineNumber] parameters to the helper, and forward them to Validate.

var instance = new { FirstName = "Gérald", LastName = "Barré" };
Helper(instance, """
    FirstName: String_0
    LastName: String_1
    """); // This string is updated when the snapshot changes

[InlineSnapshotAssertion(nameof(expected))] // name of the parameter that contains the snapshot
static void Helper(object data, string expected, [CallerFilePath] string? filePath = null, [CallerLineNumber] int lineNumber = -1)
{
    InlineSnapshot
        .WithSerializer(options => options.ScrubValue<string>())
        .Validate(data, expected, filePath, lineNumber);
}

When the snapshot changes, the library updates the expected argument of the call to Helper in the test.

Without the forwarded caller information, the location points inside the helper instead of its caller: the update fails and asks you to add the parameters. The helper can be a local function, as above, or a regular method.

The helper can also be an extension method. The library reads the receiver of the call to tell the extension syntax (value.Check("...")) from a static call (HelperExtensions.Check(value, "...")), including a static call through a using alias declared in the same file. When the receiver could be either a value or a type, such as an alias declared in another file by a global using, and two arguments hold the old snapshot, the update fails rather than changing the input of the test: name the snapshot argument (expected: "...") so it can be found.