GH-48629: [R] Add test coverage for joins with duplicate columns with removing a todo

[HyukjinKwon]

Rationale for this change

Two TODOs in test-dplyr-join.R (lines 191-192) requested test coverage for edge cases in join operations. These TODOs were added in commit c273ea7.

What changes are included in this PR?

Added one test case to r/tests/testthat/test-dplyr-join.R for duplicate columns, and added a comment about type casting because it seems it disallows the type cast. Here is example error message:

══ Failed tests ════════════════════════════════════════════════════════════════
── Error ('test-dplyr-join.R:238:3'): joins with type casting between int and float ──
Error in `compute.arrow_dplyr_query(x)`: Invalid: Incompatible data types for corresponding join field keys: FieldRef.Name(x) of type int32 and FieldRef.Name(x) of type double
Backtrace:
     ▆
  1. ├─arrow:::compare_dplyr_binding(...) at test-dplyr-join.R:238:3
  2. │ ├─testthat::expect_warning(...) at ./helper-expectation.R:95:3
  3. │ │ └─testthat:::expect_condition_matching_(...)
  4. │ │   └─testthat:::quasi_capture(...)
  5. │ │     ├─testthat (local) .capture(...)
  6. │ │     │ └─base::withCallingHandlers(...)
  7. │ │     └─rlang::eval_bare(quo_get_expr(.quo), quo_get_env(.quo))
  8. │ └─rlang::eval_tidy(expr, rlang::new_data_mask(rlang::env(.input = arrow_table(tbl))))
  9. ├─dplyr::collect(left_join(.input, right_float, by = "x"))
 10. └─arrow:::collect.arrow_dplyr_query(...)
 11.   └─arrow:::compute.arrow_dplyr_query(x)
 12.     └─base::tryCatch(...)
 13.       └─base (local) tryCatchList(expr, classes, parentenv, handlers)
 14.         └─base (local) tryCatchOne(expr, names, parentenv, handlers[[1L]])
 15.           └─value[[3L]](cond)
 16.             └─arrow:::augment_io_error_msg(e, call, schema = schema())
 17.               └─rlang::abort(msg, call = call)

Therefore this PR removes that todo.

Are these changes tested?

Yes, tests were added.

Are there any user-facing changes?

No, test-only.

• GitHub Issue: [R] Add test coverage for joins with duplicate columns #48629

[github-actions]

⚠️ GitHub issue #48629 has been automatically assigned in GitHub to PR creator.