Fix typos in testthat tests (#2632)

Author: pkq

tests/testthat/test-aes.r

@@ -93,7 +93,7 @@ test_that("quosures are squashed when creating default label for a mapping", {
   expect_identical(p$labels$x, "identity(cyl)")
 })
 
-test_that("labelling doesn't cause error if aesthetic is nul", {
+test_that("labelling doesn't cause error if aesthetic is NULL", {
   p <- ggplot(mtcars) + aes(x = NULL)
   expect_null(p$labels$x)
 })

tests/testthat/test-scale-discrete.R

@@ -48,7 +48,7 @@ test_that("NAs translated/preserved for non-position scales", {
 
 # Ranges ------------------------------------------------------------------
 
-test_that("discrete ranges also encompas continuous values", {
+test_that("discrete ranges also encompass continuous values", {
   df <- data.frame(x1 = c("a", "b", "c"), x2 = c(0, 2, 4), y = 1:3)
 
   base <- ggplot(df, aes(y = y)) + scale_x_discrete()

tests/testthat/test-scales.r

@@ -1,6 +1,6 @@
 context("Scales")
 
-test_that("buidling a plot does not affect its scales", {
+test_that("building a plot does not affect its scales", {
   dat <- data.frame(x = rnorm(20), y = rnorm(20))
 
   p <- ggplot(dat, aes(x, y)) + geom_point()