Provide mocking for S3/S4 methods and R6 classes

[hadley]

New local_mocked_s3_method(), local_mocked_s4_method(), and local_mocked_r6_class() allow you to mock S3 and S4 methods and R6 classes.

Fixes #1892. Fixes #1916.

[EmilHvitfeldt]

looking good!

[claude]

Claude finished @hadley's task —— View job

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Code Review

• Read main implementation file R/mock-oo.R
• Review test file and snapshots
• Check for potential bugs, edge cases, error handling
• Provide minimal feedback

Issues Found

Bug in R6 mocking (line 94): The string interpolation "{class$classname}" won't work as intended. In R, this creates a literal string "{class$classname}" rather than interpolating the value. Should be:

local_mocked_bindings(!!class$classname := mocked_class, .env = frame)

or

name <- class$classname
local_mocked_bindings("{name}" := mocked_class, .env = frame)

Unused variable: df in test-mock-oo.R (noted by reviewer but not addressed).

Otherwise the implementation looks solid - good input validation, proper cleanup with withr::defer, and comprehensive test coverage.