add tests to verify existing behaviour of combine_vars()

Author: paleolimbot

tests/testthat/test-facet-.r

@@ -206,6 +206,80 @@ test_that("facet gives clear error if ", {
 
 # Variable combinations ---------------------------------------------------
 
+test_that("zero-length vars in combine_vars() generates zero combinations", {
+  df <- data_frame(letter = c("a", "b"))
+  expect_equal(nrow(combine_vars(list(df), vars = vars())), 0)
+  expect_equal(ncol(combine_vars(list(df), vars = vars())), 0)
+})
+
+test_that("at least one layer must contain all facet variables in combine_vars()", {
+  df <- data_frame(letter = c("a", "b"))
+  expect_silent(combine_vars(list(df), vars = vars(letter = letter)))
+  expect_error(
+    combine_vars(list(df), vars = vars(letter = number)),
+    "At least one layer"
+  )
+})
+
+test_that("at least one combination must exist in combine_vars()", {
+  df <- data_frame(letter = character(0))
+  expect_error(
+    combine_vars(list(df), vars = vars(letter = letter)),
+    "Faceting variables must have at least one value"
+  )
+})
+
+test_that("combine_vars() generates the correct combinations", {
+  df_one <- data_frame(
+    letter = c("a", "b"),
+    number = c(1, 2),
+    boolean = c(TRUE, FALSE),
+    factor = factor(c("level1", "level2"))
+  )
+
+  df_all <- expand.grid(
+    letter = c("a", "b"),
+    number = c(1, 2),
+    boolean = c(TRUE, FALSE),
+    factor = factor(c("level1", "level2")),
+    stringsAsFactors = FALSE
+  )
+
+  vars_all <- vars(letter = letter, number =  number, boolean = boolean, factor = factor)
+
+  expect_equivalent(
+    combine_vars(list(df_one), vars = vars_all),
+    df_one
+  )
+
+  expect_equivalent(
+    combine_vars(list(df_all), vars = vars_all),
+    df_all
+  )
+
+  # with drop = FALSE the rows are ordered in the opposite order
+  # NAs are dropped with drop = FALSE (except for NA factor values);
+  # NAs are kept with with drop = TRUE
+  # drop keeps all combinations of data, regardless of the combinations in which
+  # they appear in the data (in addition to keeping unused factor levels)
+  expect_equivalent(
+    combine_vars(list(df_one), vars = vars_all, drop = FALSE),
+    df_all[order(df_all$letter, df_all$number, df_all$boolean, df_all$factor), ]
+  )
+})
+
+test_that("drop = FALSE in combine_vars() keeps unused factor levels", {
+  df <- data_frame(x = factor("a", levels = c("a", "b")))
+  expect_equivalent(
+    combine_vars(list(df), vars = vars(x = x), drop = TRUE),
+    data_frame(x = factor("a"))
+  )
+  expect_equivalent(
+    combine_vars(list(df), vars = vars(x = x), drop = FALSE),
+    data_frame(x = factor(c("a", "b")))
+  )
+})
+
 test_that("combine_vars() generates the correct combinations with multiple data frames", {
   df <- expand.grid(letter = c("a", "b"), number = c(1, 2), boolean = c(TRUE, FALSE))
 
@@ -228,7 +302,6 @@ test_that("combine_vars() generates the correct combinations with multiple data
   )
 })
 
-
 # Visual tests ------------------------------------------------------------
 
 test_that("facet labels respect both justification and margin arguments", {