diff --git a/.github/workflows/render-rmarkdown.yml b/.github/workflows/render-rmarkdown.yml
new file mode 100644
index 0000000..51ba8ea
--- /dev/null
+++ b/.github/workflows/render-rmarkdown.yml
@@ -0,0 +1,37 @@
+# Workflow derived from https://github.com/r-lib/actions/tree/v2/examples
+# Need help debugging build failures? Start at https://github.com/r-lib/actions#where-to-find-help
+on:
+  push:
+    paths: ['**.Rmd']
+
+name: render-rmarkdown.yaml
+
+permissions: read-all
+
+jobs:
+  render-rmarkdown:
+    runs-on: ubuntu-latest
+    env:
+      GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}
+    permissions:
+      contents: write
+    steps:
+      - name: Checkout repo
+        uses: actions/checkout@v4
+        with:
+          fetch-depth: 0
+
+      - uses: r-lib/actions/setup-pandoc@v2
+
+      - uses: r-lib/actions/setup-r@v2
+
+      - uses: r-lib/actions/setup-renv@v2
+
+      - name: Render Rmarkdown files and Commit Results
+        run: |
+          RMD_PATH=($(git diff --name-only ${{ github.event.before }} ${{ github.sha }} | grep '[.]Rmd$'))
+          Rscript -e 'for (f in commandArgs(TRUE)) if (file.exists(f)) rmarkdown::render(f)' ${RMD_PATH[*]}
+          git config --local user.name "$GITHUB_ACTOR"
+          git config --local user.email "$GITHUB_ACTOR@users.noreply.github.com"
+          git commit ${RMD_PATH[*]/.Rmd/.md} -m 'Re-build Rmarkdown files' || echo "No changes to commit"
+          git push origin || echo "No changes to commit"
diff --git a/.lintr b/.lintr
index e35041c..cc20872 100644
--- a/.lintr
+++ b/.lintr
@@ -11,4 +11,3 @@ exclusions: list(
 exclude: "# Exclude Linting|#\\s?nolint"
 exclude_start: "# Begin Exclude Linting|#\\s?nolint-start"
 exclude_end: "# End Exclude Linting|#\\s?nolint-end"
-
diff --git a/README.Rmd b/README.Rmd
index ffb1a17..3865d35 100644
--- a/README.Rmd
+++ b/README.Rmd
@@ -99,7 +99,7 @@ sub_set %>%
 You can also use the `summary()` function to get some basic statistics about your SPC data frame.
 The function prints the SPC options, and then returns the summarised results as a table:
 
-```r
+```{r}
 summary <- sub_set %>%
   ptd_spc(
     value_field = breaches,
@@ -112,7 +112,7 @@ summary <- sub_set %>%
 
 You could assign this summary table to a variable and use it later:
 
-```r
+```{r}
 summary$variation_type
 summary$assurance_type
 ```
diff --git a/tests/testthat/test-ptd_create_ggplot.R b/tests/testthat/test-ptd_create_ggplot.R
index e3ac5dc..e490523 100644
--- a/tests/testthat/test-ptd_create_ggplot.R
+++ b/tests/testthat/test-ptd_create_ggplot.R
@@ -1,424 +1,424 @@
-library(testthat)
-library(mockery)
-library(ggplot2, warn.conflicts = FALSE)
-
-# ptd_create_ggplot() ----
-test_that("it raises an error if unknown arguments are passed", {
-  expect_warning(
-    try(
-      ptd_create_ggplot(NULL, X = 1, Y = 2),
-      silent = TRUE
-    ),
-    paste0(
-      "Unknown arguments provided by plot: X, Y.\n",
-      "Check for common spelling mistakes in arguments."
-    ),
-    fixed = TRUE
-  )
-})
-
-test_that("it raises an error is x is not a ptd_spc_df object", {
-  expect_error(
-    ptd_create_ggplot(data.frame(x = 1, y = 2)),
-    "x argument must be an 'ptd_spc_df' object, created by ptd_spc()."
-  )
-})
-
-test_that("it calls ptd_validate_plot_options", {
-  m <- mock(stop())
-  stub(ptd_create_ggplot, "ptd_validate_plot_options", m)
-  stub(ptd_create_ggplot, "match.arg", identity)
-
-  try(
-    ptd_create_ggplot(
-      ptd_spc(data.frame(x = Sys.Date() + 1:20, y = rnorm(20)), "y", "x"),
-      "point_size",
-      "percentage_y_axis",
-      "main_title",
-      "x_axis_label",
-      "y_axis_label",
-      "fixed_x_axis_multiple",
-      "fixed_y_axis_multiple",
-      "x_axis_date_format",
-      "x_axis_breaks",
-      "y_axis_breaks",
-      "limit_annotations",
-      "icons_size",
-      "icons_position",
-      "colours",
-      "theme_override",
-      "break_lines"
-    ),
-    silent = TRUE
-  )
-
-  expect_called(m, 1)
-  expect_args(
-    m, 1,
-    "point_size",
-    "percentage_y_axis",
-    "main_title",
-    "x_axis_label",
-    "y_axis_label",
-    "fixed_x_axis_multiple",
-    "fixed_y_axis_multiple",
-    "x_axis_date_format",
-    "x_axis_breaks",
-    "y_axis_breaks",
-    "limit_annotations",
-    "icons_size",
-    "icons_position",
-    "colours",
-    "theme_override",
-    "break_lines"
-  )
-})
-
-test_that("it returns a ggplot object", {
-  set.seed(123)
-  d <- data.frame(x = as.Date("2020-01-01") + 1:20, y = rnorm(20))
-  s <- ptd_spc(d, "y", "x")
-  p <- ptd_create_ggplot(s)
-
-  expect_s3_class(p, c("gg", "ggplot"))
-  expect_length(p$layers, 8)
-  expect_equal(
-    p$labels,
-    list(
-      x = "X",
-      y = "Y",
-      group = NULL,
-      title = "SPC Chart of Y, starting 02/01/2020",
-      caption = NULL,
-      colour = "point_colour",
-      type = "type",
-      icon = "icon"
-    )
-  )
-})
-
-test_that("it facets the plot if facet_field is set", {
-  set.seed(123)
-  d <- data.frame(
-    x = as.Date("2020-01-01") + 1:20,
-    y = rnorm(20),
-    g = rep(c(1, 2), each = 10)
-  )
-
-  withr::with_options(list(ptd_spc.warning_threshold = 10), {
-    s1 <- ptd_spc(d, "y", "x")
-    p1 <- ptd_create_ggplot(s1)
-    expect_equal(p1$facet$vars(), character())
-
-    s2 <- ptd_spc(d, "y", "x", facet_field = "g")
-    p2 <- ptd_create_ggplot(s2)
-    expect_equal(p2$facet$vars(), "f")
-  })
-})
-
-test_that("it sets the x_axis_breaks correctly", {
-  m <- mock()
-  stub(ptd_create_ggplot, "ggplot2::scale_x_datetime", m)
-
-  set.seed(123)
-  d <- data.frame(x = as.POSIXct("2020-01-01") + 1:20, y = rnorm(20))
-  s <- ptd_spc(d, "y", "x")
-
-  attr(d$x, "tzone") <- ""
-
-  # no breaks set
-  p1 <- ptd_create_ggplot(s)
-  p2 <- ptd_create_ggplot(s, x_axis_breaks = "3 days")
-  p3 <- ptd_create_ggplot(s, x_axis_date_format = "%Y-%m-%d")
-  p4 <- ptd_create_ggplot(s, x_axis_breaks = "3 days", x_axis_date_format = "%Y-%m-%d")
-
-  expect_called(m, 4)
-  expect_args(m, 1, breaks = d$x, date_labels = "%d/%m/%y")
-  expect_args(m, 2, date_breaks = "3 days", date_labels = "%d/%m/%y")
-  expect_args(m, 3, breaks = d$x, date_labels = "%Y-%m-%d")
-  expect_args(m, 4, date_breaks = "3 days", date_labels = "%Y-%m-%d")
-})
-
-test_that("it sets x_axis_label correctly", {
-  set.seed(123)
-  d <- data.frame(x = as.Date("2020-01-01") + 1:20, y = rnorm(20))
-  s <- ptd_spc(d, "y", "x")
-
-  p1 <- ptd_create_ggplot(s)
-  expect_equal(p1$labels$x, "X")
-
-  p2 <- ptd_create_ggplot(s, x_axis_label = "X Axis Label")
-  expect_equal(p2$labels$x, "X Axis Label")
-})
-
-test_that("it sets y_axis_label correctly", {
-  set.seed(123)
-  d <- data.frame(x = as.Date("2020-01-01") + 1:20, y = rnorm(20))
-  s <- ptd_spc(d, "y", "x")
-
-  p1 <- ptd_create_ggplot(s)
-  expect_equal(p1$labels$y, "Y")
-
-  p2 <- ptd_create_ggplot(s, y_axis_label = "Y Axis Label")
-  expect_equal(p2$labels$y, "Y Axis Label")
-})
-
-test_that("it sets scales correctly in a faceted plot", {
-  set.seed(123)
-  d <- data.frame(
-    x = as.Date("2020-01-01") + 1:20,
-    y = rnorm(20),
-    g = rep(c(1, 2), each = 10)
-  )
-
-  withr::with_options(list(ptd_spc.warning_threshold = 10), {
-    s <- ptd_spc(d, "y", "x", facet_field = "g")
-  })
-
-  p1 <- ptd_create_ggplot(s)
-  expect_false(p1$facet$params$free$x)
-  expect_false(p1$facet$params$free$y)
-
-  p2 <- ptd_create_ggplot(s, fixed_x_axis_multiple = FALSE)
-  expect_true(p2$facet$params$free$x)
-  expect_false(p2$facet$params$free$y)
-
-  p3 <- ptd_create_ggplot(s, fixed_y_axis_multiple = FALSE)
-  expect_false(p3$facet$params$free$x)
-  expect_true(p3$facet$params$free$y)
-
-  p4 <- ptd_create_ggplot(s, fixed_x_axis_multiple = FALSE, fixed_y_axis_multiple = FALSE)
-  expect_true(p4$facet$params$free$x)
-  expect_true(p4$facet$params$free$y)
-
-  p5 <- ptd_create_ggplot(s, fixed_x_axis_multiple = TRUE, fixed_y_axis_multiple = TRUE)
-  expect_false(p5$facet$params$free$x)
-  expect_false(p5$facet$params$free$y)
-})
-
-test_that("it creates a secondary y axis with percentage scales", {
-  set.seed(123)
-  d <- data.frame(x = as.Date("2020-01-01") + 1:20, y = rnorm(20))
-  s <- ptd_spc(d, "y", "x")
-
-  sec_breaks <- s |>
-    dplyr::select(all_of(c("lpl", "mean_col", "upl"))) |>
-    dplyr::slice_head(n = 1) |>
-    unlist() |>
-    unname()
-
-  p1 <- s |>
-    ptd_create_ggplot(percentage_y_axis = TRUE, label_limits = TRUE)
-  expect_equal(
-    round(sec_breaks, 3),
-    round(p1$scales$scales[[3]]$secondary.axis$breaks, 3)
-  )
-  p2 <- s |>
-    ptd_create_ggplot(percentage_y_axis = TRUE, y_axis_breaks = 0.5, label_limits = TRUE)
-  expect_equal(
-    round(sec_breaks, 3),
-    round(p2$scales$scales[[3]]$secondary.axis$breaks, 3)
-  )
-})
-
-test_that("it creates a secondary y axis with integer scales", {
-  set.seed(123)
-  d <- data.frame(x = as.Date("2020-01-01") + 1:20, y = rnorm(20))
-  s <- ptd_spc(d, "y", "x")
-
-  sec_breaks <- s |>
-    dplyr::select(all_of(c("lpl", "mean_col", "upl"))) |>
-    dplyr::slice_head(n = 1) |>
-    unlist() |>
-    unname()
-
-  p1 <- ptd_create_ggplot(s, percentage_y_axis = FALSE, label_limits = TRUE)
-  expect_equal(p1$scales$scales[[3]]$secondary.axis$breaks, sec_breaks)
-
-  p2 <- ptd_create_ggplot(s, y_axis_breaks = 1, label_limits = TRUE)
-  expect_equal(p2$scales$scales[[3]]$secondary.axis$breaks, sec_breaks)
-})
-
-test_that("it sets the y-axis if y_axis_breaks is provided", {
-  set.seed(123)
-  d <- data.frame(x = as.Date("2020-01-01") + 1:20, y = rnorm(20))
-  s <- ptd_spc(d, "y", "x")
-
-  p1 <- ptd_create_ggplot(s, y_axis_breaks = 1)
-  expect_true(all(diff(p1$scales$scales[[3]]$breaks) == 1))
-
-  p2 <- ptd_create_ggplot(s, y_axis_breaks = 0.5)
-  expect_true(all(diff(p2$scales$scales[[3]]$breaks) == 0.5))
-})
-
-test_that("it adds theme_override to the plot", {
-  set.seed(123)
-  d <- data.frame(x = as.Date("2020-01-01") + 1:20, y = rnorm(20))
-  s <- ptd_spc(d, "y", "x")
-
-  p1 <- ptd_create_ggplot(s)
-  expect_equal(p1$theme$panel.background$fill, NULL)
-
-  p2 <- s |>
-    ptd_create_ggplot(
-      theme_override = ggplot2::theme(panel.background = ggplot2::element_rect("black")) # nolint
-    )
-  expect_equal(p2$theme$panel.background$fill, "black")
-})
-
-test_that("it breaks lines", {
-  set.seed(123)
-
-  d <- data.frame(x = as.Date("2020-01-01") + 1:20, y = rnorm(20))
-  withr::with_options(list(ptd_spc.warning_threshold = 10), {
-    s <- ptd_spc(d, "y", "x", rebase = as.Date("2020-01-01") + 11)
-  })
-
-  p1 <- ptd_create_ggplot(s)
-  expect_null(p1$mapping$group)
-  expect_equal(rlang::eval_tidy(p1$layers[[1]]$mapping$group), rep(0:1, each = 10))
-  expect_equal(rlang::eval_tidy(p1$layers[[2]]$mapping$group), rep(0:1, each = 10))
-  expect_equal(rlang::eval_tidy(p1$layers[[5]]$mapping$group), rep(0:1, each = 10))
-  expect_equal(rlang::eval_tidy(p1$layers[[6]]$mapping$group), rep(0:1, each = 10))
-
-  p2 <- ptd_create_ggplot(s, break_lines = "limits")
-  expect_equal(rlang::eval_tidy(p2$layers[[1]]$mapping$group), rep(0:1, each = 10))
-  expect_equal(rlang::eval_tidy(p2$layers[[2]]$mapping$group), rep(0:1, each = 10))
-  expect_equal(rlang::eval_tidy(p2$layers[[5]]$mapping$group), rep(0:1, each = 10))
-  expect_equal(rlang::eval_tidy(p2$layers[[6]]$mapping$group), 0)
-
-  p3 <- ptd_create_ggplot(s, break_lines = "process")
-  expect_equal(rlang::eval_tidy(p3$layers[[1]]$mapping$group), 0)
-  expect_equal(rlang::eval_tidy(p3$layers[[2]]$mapping$group), 0)
-  expect_equal(rlang::eval_tidy(p3$layers[[5]]$mapping$group), 0)
-  expect_equal(rlang::eval_tidy(p3$layers[[6]]$mapping$group), rep(0:1, each = 10))
-
-  p4 <- ptd_create_ggplot(s, break_lines = "none")
-  expect_equal(rlang::eval_tidy(p4$layers[[1]]$mapping$group), 0)
-  expect_equal(rlang::eval_tidy(p4$layers[[2]]$mapping$group), 0)
-  expect_equal(rlang::eval_tidy(p4$layers[[5]]$mapping$group), 0)
-  expect_equal(rlang::eval_tidy(p4$layers[[6]]$mapping$group), 0)
-})
-
-test_that("it sets the colour of the points based on the type", {
-  m <- mock()
-
-  stub(ptd_create_ggplot, "ggplot2::scale_colour_manual", m)
-
-  set.seed(123)
-  d <- data.frame(x = as.Date("2020-01-01") + seq(20L), y = rnorm(20L)) |>
-    # introduce some special cause variation!
-    dplyr::mutate(
-      across("y", \(y) dplyr::if_else(.data[["x"]] > "2020-01-15", y + 0.5, y))
-    )
-
-  colours_neutral <- list(
-    common_cause              = "#a6a6a6", # grey
-    special_cause_neutral     = "#490092" # purple
-  )
-
-  colours_otherwise <- list(
-    common_cause              = "#a6a6a6", # grey
-    special_cause_improvement = "#00b0f0", # blue
-    special_cause_concern     = "#e46c0a" # orange
-  )
-
-  # case 1: improvement_direction = neutral
-  s1 <- ptd_spc(d, "y", "x", improvement_direction = "neutral")
-  p1 <- ptd_create_ggplot(s1)
-  # case 2: improvement_direction = "increase"
-  s2 <- ptd_spc(d, "y", "x", improvement_direction = "increase")
-  p2 <- ptd_create_ggplot(s2)
-  # case 3: improvement_direction = "decrease"
-  s3 <- ptd_spc(d, "y", "x", improvement_direction = "decrease")
-  p3 <- ptd_create_ggplot(s3)
-
-  expect_called(m, 3)
-  expect_args(m, 1, values = colours_neutral, labels = ptd_title_case)
-  expect_args(m, 2, values = colours_otherwise, labels = ptd_title_case)
-})
-
-test_that("it sets the main title correctly", {
-  d <- data.frame(x = as.Date("2020-01-01") + 1:20, y = rnorm(20), z = rnorm(20))
-  s <- ptd_spc(d, "y", "x")
-
-  p1 <- ptd_create_ggplot(s)
-  expect_equal(p1$labels$title, "SPC Chart of Y, starting 02/01/2020")
-
-  p2 <- ptd_create_ggplot(s, main_title = "Thing")
-  expect_equal(p2$labels$title, "Thing")
-})
-
-test_that("a plot with short rebase group has a warning caption", {
-  d <- data.frame(x = as.Date("2020-01-01") + 1:40, y = rnorm(40))
-  # rebase at midpoint, no short groups
-  s1 <- ptd_spc(d, "y", "x", rebase = as.Date("2020-01-20"))
-  # rebase close to end of points
-  s2 <- suppressWarnings(ptd_spc(d, "y", "x", rebase = as.Date("2020-02-02")))
-
-  p1 <- ptd_create_ggplot(s1)
-  expect_equal(p1$labels$caption, NULL)
-
-  p2 <- ptd_create_ggplot(s2)
-  expect_equal(
-    p2$labels$caption,
-    paste0(
-      "Some trial limits created by groups of fewer than 12 points exist.\n",
-      "These will become more reliable as more data is added."
-    )
-  )
-})
-
-test_that("it doesn't add icons if icons_position is 'none'", {
-  m <- mock()
-  stub(ptd_create_ggplot, "geom_ptd_icon", m)
-
-  set.seed(123)
-  d <- data.frame(
-    x = as.Date("2020-01-01") + 1:20,
-    y = rnorm(20)
-  )
-
-  s1 <- ptd_spc(d, "y", "x", target = 0.5)
-  p1 <- ptd_create_ggplot(s1, icons_position = "top right")
-  p2 <- ptd_create_ggplot(s1, icons_position = "none")
-
-  expect_called(m, 1)
-})
-
-# plot() ----
-test_that("it calls ptd_create_ggplot()", {
-  set.seed(123)
-  s <- ptd_spc(
-    data.frame(
-      x = Sys.Date() + 1:20,
-      y = rnorm(20)
-    ),
-    "y", "x"
-  )
-
-  m <- mock()
-  stub(plot.ptd_spc_df, "ptd_create_ggplot", m)
-  stub(plot.ptd_spc_df, "ptd_spc_colours", "colours")
-  plot(s, main_title = "a", x_axis_label = "b", y_axis_label = "c")
-
-  expect_called(m, 1)
-  expect_args(m, 1, s,
-    point_size = 4,
-    percentage_y_axis = FALSE,
-    main_title = "a",
-    x_axis_label = "b",
-    y_axis_label = "c",
-    fixed_x_axis_multiple = TRUE,
-    fixed_y_axis_multiple = TRUE,
-    x_axis_date_format = "%d/%m/%y",
-    x_axis_breaks = NULL,
-    y_axis_breaks = NULL,
-    limit_annotations = FALSE,
-    icons_size = 8L,
-    icons_position = c("top right", "bottom right", "bottom left", "top left", "none"),
-    colours = "colours",
-    theme_override = NULL,
-    break_lines = "both"
-  )
-})
+library(testthat)
+library(mockery)
+library(ggplot2, warn.conflicts = FALSE)
+
+# ptd_create_ggplot() ----
+test_that("it raises an error if unknown arguments are passed", {
+  expect_warning(
+    try(
+      ptd_create_ggplot(NULL, X = 1, Y = 2),
+      silent = TRUE
+    ),
+    paste0(
+      "Unknown arguments provided by plot: X, Y.\n",
+      "Check for common spelling mistakes in arguments."
+    ),
+    fixed = TRUE
+  )
+})
+
+test_that("it raises an error is x is not a ptd_spc_df object", {
+  expect_error(
+    ptd_create_ggplot(data.frame(x = 1, y = 2)),
+    "x argument must be an 'ptd_spc_df' object, created by ptd_spc()."
+  )
+})
+
+test_that("it calls ptd_validate_plot_options", {
+  m <- mock(stop())
+  stub(ptd_create_ggplot, "ptd_validate_plot_options", m)
+  stub(ptd_create_ggplot, "match.arg", identity)
+
+  try(
+    ptd_create_ggplot(
+      ptd_spc(data.frame(x = Sys.Date() + seq(20L), y = rnorm(20L)), "y", "x"),
+      "point_size",
+      "percentage_y_axis",
+      "main_title",
+      "x_axis_label",
+      "y_axis_label",
+      "fixed_x_axis_multiple",
+      "fixed_y_axis_multiple",
+      "x_axis_date_format",
+      "x_axis_breaks",
+      "y_axis_breaks",
+      "limit_annotations",
+      "icons_size",
+      "icons_position",
+      "colours",
+      "theme_override",
+      "break_lines"
+    ),
+    silent = TRUE
+  )
+
+  expect_called(m, 1)
+  expect_args(
+    m, 1,
+    "point_size",
+    "percentage_y_axis",
+    "main_title",
+    "x_axis_label",
+    "y_axis_label",
+    "fixed_x_axis_multiple",
+    "fixed_y_axis_multiple",
+    "x_axis_date_format",
+    "x_axis_breaks",
+    "y_axis_breaks",
+    "limit_annotations",
+    "icons_size",
+    "icons_position",
+    "colours",
+    "theme_override",
+    "break_lines"
+  )
+})
+
+test_that("it returns a ggplot object", {
+  set.seed(123)
+  d <- data.frame(x = as.Date("2020-01-01") + seq(20L), y = rnorm(20L))
+  s <- ptd_spc(d, "y", "x")
+  p <- ptd_create_ggplot(s)
+
+  expect_s3_class(p, c("gg", "ggplot"))
+  expect_length(p$layers, 8)
+  expect_equal(
+    p$labels,
+    list(
+      x = "X",
+      y = "Y",
+      group = NULL,
+      title = "SPC Chart of Y, starting 02/01/2020",
+      caption = NULL,
+      colour = "point_colour",
+      type = "type",
+      icon = "icon"
+    )
+  )
+})
+
+test_that("it facets the plot if facet_field is set", {
+  set.seed(123)
+  d <- data.frame(
+    x = as.Date("2020-01-01") + 1:20,
+    y = rnorm(20L),
+    g = rep(c(1L, 2L), each = 10L)
+  )
+
+  withr::with_options(list(ptd_spc.warning_threshold = 10), {
+    s1 <- ptd_spc(d, "y", "x")
+    p1 <- ptd_create_ggplot(s1)
+    expect_equal(p1$facet$vars(), character())
+
+    s2 <- ptd_spc(d, "y", "x", facet_field = "g")
+    p2 <- ptd_create_ggplot(s2)
+    expect_equal(p2$facet$vars(), "f")
+  })
+})
+
+test_that("it sets the x_axis_breaks correctly", {
+  m <- mock()
+  stub(ptd_create_ggplot, "ggplot2::scale_x_datetime", m)
+
+  set.seed(123)
+  d <- data.frame(x = as.POSIXct("2020-01-01") + seq(20L), y = rnorm(20L))
+  s <- ptd_spc(d, "y", "x")
+
+  attr(d$x, "tzone") <- ""
+
+  # no breaks set
+  p1 <- ptd_create_ggplot(s)
+  p2 <- ptd_create_ggplot(s, x_axis_breaks = "3 days")
+  p3 <- ptd_create_ggplot(s, x_axis_date_format = "%Y-%m-%d")
+  p4 <- ptd_create_ggplot(s, x_axis_breaks = "3 days", x_axis_date_format = "%Y-%m-%d")
+
+  expect_called(m, 4)
+  expect_args(m, 1, breaks = d$x, date_labels = "%d/%m/%y")
+  expect_args(m, 2, date_breaks = "3 days", date_labels = "%d/%m/%y")
+  expect_args(m, 3, breaks = d$x, date_labels = "%Y-%m-%d")
+  expect_args(m, 4, date_breaks = "3 days", date_labels = "%Y-%m-%d")
+})
+
+test_that("it sets x_axis_label correctly", {
+  set.seed(123)
+  d <- data.frame(x = as.Date("2020-01-01") + seq(20L), y = rnorm(20L))
+  s <- ptd_spc(d, "y", "x")
+
+  p1 <- ptd_create_ggplot(s)
+  expect_equal(p1$labels$x, "X")
+
+  p2 <- ptd_create_ggplot(s, x_axis_label = "X Axis Label")
+  expect_equal(p2$labels$x, "X Axis Label")
+})
+
+test_that("it sets y_axis_label correctly", {
+  set.seed(123)
+  d <- data.frame(x = as.Date("2020-01-01") + seq(20L), y = rnorm(20L))
+  s <- ptd_spc(d, "y", "x")
+
+  p1 <- ptd_create_ggplot(s)
+  expect_equal(p1$labels$y, "Y")
+
+  p2 <- ptd_create_ggplot(s, y_axis_label = "Y Axis Label")
+  expect_equal(p2$labels$y, "Y Axis Label")
+})
+
+test_that("it sets scales correctly in a faceted plot", {
+  set.seed(123)
+  d <- data.frame(
+    x = as.Date("2020-01-01") + seq(20L),
+    y = rnorm(20L),
+    g = rep(c(1L, 2L), each = 10L)
+  )
+
+  withr::with_options(list(ptd_spc.warning_threshold = 10), {
+    s <- ptd_spc(d, "y", "x", facet_field = "g")
+  })
+
+  p1 <- ptd_create_ggplot(s)
+  expect_false(p1$facet$params$free$x)
+  expect_false(p1$facet$params$free$y)
+
+  p2 <- ptd_create_ggplot(s, fixed_x_axis_multiple = FALSE)
+  expect_true(p2$facet$params$free$x)
+  expect_false(p2$facet$params$free$y)
+
+  p3 <- ptd_create_ggplot(s, fixed_y_axis_multiple = FALSE)
+  expect_false(p3$facet$params$free$x)
+  expect_true(p3$facet$params$free$y)
+
+  p4 <- ptd_create_ggplot(s, fixed_x_axis_multiple = FALSE, fixed_y_axis_multiple = FALSE)
+  expect_true(p4$facet$params$free$x)
+  expect_true(p4$facet$params$free$y)
+
+  p5 <- ptd_create_ggplot(s, fixed_x_axis_multiple = TRUE, fixed_y_axis_multiple = TRUE)
+  expect_false(p5$facet$params$free$x)
+  expect_false(p5$facet$params$free$y)
+})
+
+test_that("it creates a secondary y axis with percentage scales", {
+  set.seed(123)
+  d <- data.frame(x = as.Date("2020-01-01") + seq(20L), y = rnorm(20L))
+  s <- ptd_spc(d, "y", "x")
+
+  sec_breaks <- s |>
+    dplyr::select(all_of(c("lpl", "mean_col", "upl"))) |>
+    dplyr::slice_head(n = 1) |>
+    unlist() |>
+    unname()
+
+  p1 <- s |>
+    ptd_create_ggplot(percentage_y_axis = TRUE, label_limits = TRUE)
+  expect_equal(
+    round(sec_breaks, 3),
+    round(p1$scales$scales[[3]]$secondary.axis$breaks, 3)
+  )
+  p2 <- s |>
+    ptd_create_ggplot(percentage_y_axis = TRUE, y_axis_breaks = 0.5, label_limits = TRUE)
+  expect_equal(
+    round(sec_breaks, 3),
+    round(p2$scales$scales[[3]]$secondary.axis$breaks, 3)
+  )
+})
+
+test_that("it creates a secondary y axis with integer scales", {
+  set.seed(123)
+  d <- data.frame(x = as.Date("2020-01-01") + seq(20L), y = rnorm(20L))
+  s <- ptd_spc(d, "y", "x")
+
+  sec_breaks <- s |>
+    dplyr::select(all_of(c("lpl", "mean_col", "upl"))) |>
+    dplyr::slice_head(n = 1) |>
+    unlist() |>
+    unname()
+
+  p1 <- ptd_create_ggplot(s, percentage_y_axis = FALSE, label_limits = TRUE)
+  expect_equal(p1$scales$scales[[3]]$secondary.axis$breaks, sec_breaks)
+
+  p2 <- ptd_create_ggplot(s, y_axis_breaks = 1, label_limits = TRUE)
+  expect_equal(p2$scales$scales[[3]]$secondary.axis$breaks, sec_breaks)
+})
+
+test_that("it sets the y-axis if y_axis_breaks is provided", {
+  set.seed(123)
+  d <- data.frame(x = as.Date("2020-01-01") + seq(20L), y = rnorm(20L))
+  s <- ptd_spc(d, "y", "x")
+
+  p1 <- ptd_create_ggplot(s, y_axis_breaks = 1)
+  expect_true(all(diff(p1$scales$scales[[3]]$breaks) == 1))
+
+  p2 <- ptd_create_ggplot(s, y_axis_breaks = 0.5)
+  expect_true(all(diff(p2$scales$scales[[3]]$breaks) == 0.5))
+})
+
+test_that("it adds theme_override to the plot", {
+  set.seed(123)
+  d <- data.frame(x = as.Date("2020-01-01") + seq(20L), y = rnorm(20L))
+  s <- ptd_spc(d, "y", "x")
+
+  p1 <- ptd_create_ggplot(s)
+  expect_equal(p1$theme$panel.background$fill, NULL)
+
+  p2 <- s |>
+    ptd_create_ggplot(
+      theme_override = ggplot2::theme(panel.background = ggplot2::element_rect("black")) # nolint
+    )
+  expect_equal(p2$theme$panel.background$fill, "black")
+})
+
+test_that("it breaks lines", {
+  set.seed(123)
+
+  d <- data.frame(x = as.Date("2020-01-01") + seq(20L), y = rnorm(20L))
+  withr::with_options(list(ptd_spc.warning_threshold = 10), {
+    s <- ptd_spc(d, "y", "x", rebase = as.Date("2020-01-01") + 11)
+  })
+
+  p1 <- ptd_create_ggplot(s)
+  expect_null(p1$mapping$group)
+  expect_equal(rlang::eval_tidy(p1$layers[[1]]$mapping$group), rep(0:1, each = 10))
+  expect_equal(rlang::eval_tidy(p1$layers[[2]]$mapping$group), rep(0:1, each = 10))
+  expect_equal(rlang::eval_tidy(p1$layers[[5]]$mapping$group), rep(0:1, each = 10))
+  expect_equal(rlang::eval_tidy(p1$layers[[6]]$mapping$group), rep(0:1, each = 10))
+
+  p2 <- ptd_create_ggplot(s, break_lines = "limits")
+  expect_equal(rlang::eval_tidy(p2$layers[[1]]$mapping$group), rep(0:1, each = 10))
+  expect_equal(rlang::eval_tidy(p2$layers[[2]]$mapping$group), rep(0:1, each = 10))
+  expect_equal(rlang::eval_tidy(p2$layers[[5]]$mapping$group), rep(0:1, each = 10))
+  expect_equal(rlang::eval_tidy(p2$layers[[6]]$mapping$group), 0)
+
+  p3 <- ptd_create_ggplot(s, break_lines = "process")
+  expect_equal(rlang::eval_tidy(p3$layers[[1]]$mapping$group), 0)
+  expect_equal(rlang::eval_tidy(p3$layers[[2]]$mapping$group), 0)
+  expect_equal(rlang::eval_tidy(p3$layers[[5]]$mapping$group), 0)
+  expect_equal(rlang::eval_tidy(p3$layers[[6]]$mapping$group), rep(0:1, each = 10))
+
+  p4 <- ptd_create_ggplot(s, break_lines = "none")
+  expect_equal(rlang::eval_tidy(p4$layers[[1]]$mapping$group), 0)
+  expect_equal(rlang::eval_tidy(p4$layers[[2]]$mapping$group), 0)
+  expect_equal(rlang::eval_tidy(p4$layers[[5]]$mapping$group), 0)
+  expect_equal(rlang::eval_tidy(p4$layers[[6]]$mapping$group), 0)
+})
+
+test_that("it sets the colour of the points based on the type", {
+  m <- mock()
+
+  stub(ptd_create_ggplot, "ggplot2::scale_colour_manual", m)
+
+  set.seed(123)
+  d <- data.frame(x = as.Date("2020-01-01") + seq(20L), y = rnorm(20L)) |>
+    # introduce some special cause variation!
+    dplyr::mutate(
+      across("y", \(y) dplyr::if_else(.data[["x"]] > "2020-01-15", y + 0.5, y))
+    )
+
+  colours_neutral <- list(
+    common_cause              = "#a6a6a6", # grey
+    special_cause_neutral     = "#490092" # purple
+  )
+
+  colours_otherwise <- list(
+    common_cause              = "#a6a6a6", # grey
+    special_cause_improvement = "#00b0f0", # blue
+    special_cause_concern     = "#e46c0a" # orange
+  )
+
+  # case 1: improvement_direction = neutral
+  s1 <- ptd_spc(d, "y", "x", improvement_direction = "neutral")
+  p1 <- ptd_create_ggplot(s1)
+  # case 2: improvement_direction = "increase"
+  s2 <- ptd_spc(d, "y", "x", improvement_direction = "increase")
+  p2 <- ptd_create_ggplot(s2)
+  # case 3: improvement_direction = "decrease"
+  s3 <- ptd_spc(d, "y", "x", improvement_direction = "decrease")
+  p3 <- ptd_create_ggplot(s3)
+
+  expect_called(m, 3)
+  expect_args(m, 1, values = colours_neutral, labels = ptd_title_case)
+  expect_args(m, 2, values = colours_otherwise, labels = ptd_title_case)
+})
+
+test_that("it sets the main title correctly", {
+  d <- data.frame(x = as.Date("2020-01-01") + seq(20L), y = rnorm(20L), z = rnorm(20L))
+  s <- ptd_spc(d, "y", "x")
+
+  p1 <- ptd_create_ggplot(s)
+  expect_equal(p1$labels$title, "SPC Chart of Y, starting 02/01/2020")
+
+  p2 <- ptd_create_ggplot(s, main_title = "Thing")
+  expect_equal(p2$labels$title, "Thing")
+})
+
+test_that("a plot with short rebase group has a warning caption", {
+  d <- data.frame(x = as.Date("2020-01-01") + seq(40L), y = rnorm(40L))
+  # rebase at midpoint, no short groups
+  s1 <- ptd_spc(d, "y", "x", rebase = as.Date("2020-01-20"))
+  # rebase close to end of points
+  s2 <- suppressWarnings(ptd_spc(d, "y", "x", rebase = as.Date("2020-02-02")))
+
+  p1 <- ptd_create_ggplot(s1)
+  expect_equal(p1$labels$caption, NULL)
+
+  p2 <- ptd_create_ggplot(s2)
+  expect_equal(
+    p2$labels$caption,
+    paste0(
+      "Some trial limits created by groups of fewer than 12 points exist.\n",
+      "These will become more reliable as more data is added."
+    )
+  )
+})
+
+test_that("it doesn't add icons if icons_position is 'none'", {
+  m <- mock()
+  stub(ptd_create_ggplot, "geom_ptd_icon", m)
+
+  set.seed(123)
+  d <- data.frame(
+    x = as.Date("2020-01-01") + seq(20L),
+    y = rnorm(20L)
+  )
+
+  s1 <- ptd_spc(d, "y", "x", target = 0.5)
+  p1 <- ptd_create_ggplot(s1, icons_position = "top right")
+  p2 <- ptd_create_ggplot(s1, icons_position = "none")
+
+  expect_called(m, 1)
+})
+
+# plot() ----
+test_that("it calls ptd_create_ggplot()", {
+  set.seed(123)
+  s <- ptd_spc(
+    data.frame(
+      x = Sys.Date() + seq(20L),
+      y = rnorm(20L)
+    ),
+    "y", "x"
+  )
+
+  m <- mock()
+  stub(plot.ptd_spc_df, "ptd_create_ggplot", m)
+  stub(plot.ptd_spc_df, "ptd_spc_colours", "colours")
+  plot(s, main_title = "a", x_axis_label = "b", y_axis_label = "c")
+
+  expect_called(m, 1)
+  expect_args(m, 1, s,
+    point_size = 4,
+    percentage_y_axis = FALSE,
+    main_title = "a",
+    x_axis_label = "b",
+    y_axis_label = "c",
+    fixed_x_axis_multiple = TRUE,
+    fixed_y_axis_multiple = TRUE,
+    x_axis_date_format = "%d/%m/%y",
+    x_axis_breaks = NULL,
+    y_axis_breaks = NULL,
+    limit_annotations = FALSE,
+    icons_size = 8,
+    icons_position = c("top right", "bottom right", "bottom left", "top left", "none"),
+    colours = "colours",
+    theme_override = NULL,
+    break_lines = "both"
+  )
+})