Refactor test-layer-positioning.R to eliminate code duplication

[Copilot]

The test file contained duplicated dummy_df creation code in two test cases (lines 13-31 and 89-107), both constructing identical test data from GitHub issue #162.

Changes

• Extracted create_issue_162_dummy_df() helper function to encapsulate shared test data
• Updated both test cases to call the helper function instead of duplicating 19 lines of setup code
• Reduces file from 117 to 104 lines while maintaining identical test behavior

# Helper function to create the dummy_df from GitHub issue #162
create_issue_162_dummy_df <- function() {
  tibble(
    row_id = c(
      "B cells", "Basophils", "Eosinophils", "Myeloid", "NK cells", "Neutrophils", "T cells",
      "B cells", "Basophils", "Eosinophils", "Myeloid", "NK cells", "Neutrophils", "T cells"
    ),
    col_id = c(rep("Control", 7), rep("Test", 7)),
    value = c(0.2000, -0.0180, 0.0983, 0.1930, 0.0934, 0.0529, -0.2090,
              0.0831, 0.00515, 0.0413, 0.0808, 0.0123, 0.0619, -0.1550),
    adj_p = c(5.81e-10, 2.72e-01, 4.46e-04, 1.44e-06, 6.43e-08, 1.08e-01, 7.65e-07,
              6.46e-02, 7.81e-01, 2.47e-01, 6.46e-02, 5.90e-01, 6.46e-02, 6.28e-03)
  ) %>% 
    mutate(col_id = fct_relevel(col_id, c("Control", "Test")))
}

test_that("layer_asterisk positions match matrix structure - using issue #162 dummy_df", {
  dummy_df <- create_issue_162_dummy_df()
  # ... rest of test
})

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Note

Streamlines test setup for layer positioning validations while keeping assertions and visuals intact.

• Adds create_issue_162_dummy_df() helper in tests/testthat/test-layer-positioning.R
• Replaces duplicated tibble construction in two tests with the helper (layer_asterisk position and visual tests)
• No logic changes to tests; maintains same expectations and vdiffr snapshot, reducing duplication and lines of code

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