test: add failing tests for check_model() theme argument bug (#851)

NEWS.md

@@ -7,6 +7,14 @@
 
 * Improved documentation for printing-methods.
 
+## Known Issues
+
+* The `theme` argument in `check_model()` currently has no effect due to a bug
+  in the **see** package's plot method. The `check_model()` function correctly
+  stores the theme attribute, but the **see** package's `plot.check_model()`
+  function does not properly handle it. This issue is tracked in #851 and
+  requires a fix in the **see** package repository.
+
 # performance 0.15.2
 
 ## Bug fixes

tests/testthat/test-check_model_theme.R

@@ -0,0 +1,227 @@
+# ==============================================================================
+# ISSUE #851: theme argument of check_model() has no effect
+# ==============================================================================
+#
+# These tests document the expected behavior of the theme argument in
+# check_model(). Currently, these tests FAIL due to bugs in the see package's
+# plot.check_model() function.
+#
+# Three main problems identified:
+# 1. Standard ggplot2 themes cause "unused arguments" errors
+# 2. Custom user-defined theme functions cannot be accessed
+# 3. Theme attribute not properly read by see package's plot method
+#
+# The actual fix needs to be implemented in the see package's
+# R/plot.check_model.R file (around lines 64-67).
+#
+# See: https://github.com/easystats/performance/issues/851
+# ==============================================================================
+
+# Test 1: Standard ggplot2 themes should work without errors
+# -----------------------------------------------------------------------------
+# PROBLEM: Currently throws "unused arguments" error because see package passes
+# hardcoded arguments (plot.title.space, axis.title.space, etc.) that don't
+# exist in standard ggplot2 themes.
+test_that("check_model accepts standard ggplot2 themes as functions", {
+  skip_if_not_installed("performance")
+  skip_if_not_installed("see")
+  skip_if_not_installed("ggplot2")
+
+  m <- lm(mpg ~ wt + cyl + gear + disp, data = mtcars)
+
+  # Test with theme_dark passed as function (not string)
+  # Explicit namespace call for clarity and to avoid conflicts
+  expect_no_error({
+    p1 <- check_model(m, theme = ggplot2::theme_dark)
+    # The plot method should handle the theme attribute correctly
+    if (requireNamespace("see", quietly = TRUE)) {
+      plot(p1)
+    }
+  })
+
+  # Test with theme_minimal
+  expect_no_error({
+    p2 <- check_model(m, theme = ggplot2::theme_minimal)
+    if (requireNamespace("see", quietly = TRUE)) {
+      plot(p2)
+    }
+  })
+
+  # Test with theme_bw
+  expect_no_error({
+    p3 <- check_model(m, theme = ggplot2::theme_bw)
+    if (requireNamespace("see", quietly = TRUE)) {
+      plot(p3)
+    }
+  })
+})
+
+
+# Test 2: Theme as string should work for backward compatibility
+# -----------------------------------------------------------------------------
+# PROBLEM: String parsing doesn't work reliably, and when it does parse,
+# it still hits the "unused arguments" error from hardcoded parameters.
+test_that("check_model accepts theme as string (backward compatibility)", {
+  skip_if_not_installed("performance")
+  skip_if_not_installed("see")
+  skip_if_not_installed("ggplot2")
+
+  m <- lm(mpg ~ wt + cyl + gear + disp, data = mtcars)
+
+  # String reference should work
+  expect_no_error({
+    p1 <- check_model(m, theme = "ggplot2::theme_dark")
+    if (requireNamespace("see", quietly = TRUE)) {
+      plot(p1)
+    }
+  })
+
+  # Test with theme_bw as string
+  expect_no_error({
+    p2 <- check_model(m, theme = "ggplot2::theme_bw")
+    if (requireNamespace("see", quietly = TRUE)) {
+      plot(p2)
+    }
+  })
+})
+
+
+# Test 3: Custom theme functions should work
+# -----------------------------------------------------------------------------
+# PROBLEM: Custom themes defined in user environment can't be accessed because
+# the see package's string parsing approach only searches package namespaces.
+test_that("check_model accepts custom theme functions from user environment", {
+  skip_if_not_installed("performance")
+  skip_if_not_installed("see")
+  skip_if_not_installed("ggplot2")
+
+  # Define custom theme in test environment
+  my_custom_theme <- function(
+    base_size = 11,
+    base_family = "",
+    base_line_size = base_size / 22,
+    base_rect_size = base_size / 22
+  ) {
+    ggplot2::theme_minimal(
+      base_size = base_size,
+      base_family = base_family,
+      base_line_size = base_line_size,
+      base_rect_size = base_rect_size
+    ) +
+      ggplot2::theme(
+        plot.title = ggplot2::element_text(size = 16, face = "bold"),
+        panel.grid.major = ggplot2::element_line(color = "gray80")
+      )
+  }
+
+  m <- lm(mpg ~ wt + cyl + gear + disp, data = mtcars)
+
+  # Custom theme function should work when passed directly
+  expect_no_error({
+    p1 <- check_model(m, theme = my_custom_theme)
+    if (requireNamespace("see", quietly = TRUE)) {
+      plot(p1)
+    }
+  })
+
+  # Also test passing custom theme to plot method's style argument
+  expect_no_error({
+    p2 <- check_model(m)
+    if (requireNamespace("see", quietly = TRUE)) {
+      plot(p2, style = my_custom_theme)
+    }
+  })
+})
+
+
+# Test 4: Theme attribute should be stored and retrieved correctly
+# -----------------------------------------------------------------------------
+# PROBLEM: The theme attribute is stored by check_model() but may not be
+# properly read by see package's plot method.
+test_that("theme attribute is stored and used correctly", {
+  skip_if_not_installed("performance")
+  skip_if_not_installed("see")
+  skip_if_not_installed("ggplot2")
+
+  m <- lm(mpg ~ wt + cyl + gear + disp, data = mtcars)
+
+  # Test with function
+  p1 <- check_model(m, theme = ggplot2::theme_dark)
+
+  # Theme should be stored as attribute
+  expect_true(!is.null(attr(p1, "theme")))
+
+  # Attribute should contain the theme
+  theme_attr <- attr(p1, "theme")
+  expect_true(is.function(theme_attr) || is.character(theme_attr))
+
+  # Validate theme more specifically
+  if (is.function(theme_attr)) {
+    expect_s3_class(theme_attr(), "theme")
+  }
+
+  # Theme should be applied when plotting
+  if (requireNamespace("see", quietly = TRUE)) {
+    expect_no_error(plot(p1))
+  }
+
+  # Test with string
+  p2 <- check_model(m, theme = "ggplot2::theme_minimal")
+  expect_true(!is.null(attr(p2, "theme")))
+  expect_identical(attr(p2, "theme"), "ggplot2::theme_minimal")
+
+  if (requireNamespace("see", quietly = TRUE)) {
+    expect_no_error(plot(p2))
+  }
+})
+
+
+# Test 5: Default theme should work when no theme specified
+# -----------------------------------------------------------------------------
+# Tests that check_model works correctly when no theme argument is provided,
+# ensuring it falls back to the default theme.
+test_that("check_model works without theme argument (default behavior)", {
+  skip_if_not_installed("performance")
+  skip_if_not_installed("see")
+
+  m <- lm(mpg ~ wt + cyl + gear + disp, data = mtcars)
+
+  # Should work with default theme
+  expect_no_error({
+    p <- check_model(m)
+    if (requireNamespace("see", quietly = TRUE)) {
+      plot(p)
+    }
+  })
+
+  # Default theme should be stored
+  p <- check_model(m)
+  expect_true(!is.null(attr(p, "theme")))
+})
+
+
+# Test 6: style argument in plot() should override theme from check_model()
+# -----------------------------------------------------------------------------
+# This tests that the plot method's style parameter can override the theme
+# set during check_model() call.
+test_that("plot style argument overrides check_model theme", {
+  skip_if_not_installed("performance")
+  skip_if_not_installed("see")
+  skip_if_not_installed("ggplot2")
+
+  m <- lm(mpg ~ wt + cyl + gear + disp, data = mtcars)
+
+  # Create with one theme
+  p <- check_model(m, theme = ggplot2::theme_dark)
+
+  # Plot with different theme - should work
+  if (requireNamespace("see", quietly = TRUE)) {
+    expect_no_error({
+      plot(p, style = ggplot2::theme_minimal)
+    })
+
+    expect_no_error({
+      plot(p, style = ggplot2::theme_bw)
+    })
+  }
+})