diff --git a/man/create_layer.Rd b/man/create_layer.Rd
index 7917e8854..81f5e33b0 100644
--- a/man/create_layer.Rd
+++ b/man/create_layer.Rd
@@ -9,9 +9,9 @@ create_layer(name = NULL, open = rlang::is_interactive())
 \arguments{
 \item{name}{Either a name without extension, or \code{NULL} to create the
 paired file based on currently open file in the script editor. If
-the R file is open, \code{use_test()} will create/open the corresponding
+the \verb{R/} file is open, \code{use_test()} will create/open the corresponding
 test file; if the test file is open, \code{use_r()} will create/open the
-corresponding R file.}
+corresponding \verb{R/} file.}
 
 \item{open}{Whether to open the file for interactive editing.}
 }
diff --git a/tests/testthat/test-assign_arg_list.R b/tests/testthat/test-assign_arg_list.R
new file mode 100644
index 000000000..7cd69dfa9
--- /dev/null
+++ b/tests/testthat/test-assign_arg_list.R
@@ -0,0 +1,11 @@
+test_that("First argument must be a list",{
+  expect_error(assign_arg_list(c(1,2,3)))
+})
+test_that("All arguments should be named",{
+  expect_error(assign_arg_list(list(1,2)))
+})
+test_that("assign_arg_list works as intended",{
+  assign_arg_list(list(a="dog",b=2))
+  expect_identical(a,"dog")
+  expect_identical(b,2)
+})
diff --git a/tests/testthat/test-df_mat_mul.R b/tests/testthat/test-df_mat_mul.R
new file mode 100644
index 000000000..fe370bd5f
--- /dev/null
+++ b/tests/testthat/test-df_mat_mul.R
@@ -0,0 +1,41 @@
+df <- data.frame(matrix(1:100, ncol = 5))
+mat <- matrix(1:4, ncol = 2)
+
+test_that("First input must be a data frame and second
+          input must be a matrix", {
+  expect_error(df_mat_mul(df,20))
+  expect_error(df_mat_mul(30,mat))
+})
+
+test_that("Argument name is a character", {
+  expect_error(df_mat_mul(df, mat, 100))
+})
+
+test_that("The length of names does not differ from the length of the number
+          of outputs" ,{
+  expect_error(df_mat_mul(df, mat, c("a","b","c"), 2:3))
+})
+
+test_that("The number of columns of the first data frame cannot differ from the
+          number of rows of the second matrix, hence preventing incompatible
+          matrix multiplication", {
+            expect_error(df_mat_mul(df, mat, "z", 1:3))
+})
+
+X <- df[c(1,4,5)]
+Z <- as.data.frame(as.matrix(df[2:3]) %*% mat)
+colnames(Z) <- c("z1","z2")
+output <- cbind(X,Z)
+
+test_that("Names are being handled properly", {
+  expect_identical(df_mat_mul(df, mat, "z", 2:3),output)
+  expect_identical(df_mat_mul(df, mat, c("z1","z2"), 2:3),output)
+})
+
+test_that("Other tidyselect functionalities are working", {
+  mult <- df_mat_mul(df, mat, "z", dplyr::num_range("X", 2:3))
+  expect_identical(mult,output)
+  expect_identical(df_mat_mul(df, mat, "z", 2, 3),output)
+  # Mismatched names should not work:
+  expect_error(df_mat_mul(df, mat, "z", dplyr::num_range("Y", 2:3)))
+})
diff --git a/tests/testthat/test-grab_names.R b/tests/testthat/test-grab_names.R
new file mode 100644
index 000000000..2e7954ab3
--- /dev/null
+++ b/tests/testthat/test-grab_names.R
@@ -0,0 +1,7 @@
+df <- data.frame(b=1,c=2,ca=3,cat=4)
+
+test_that("Names are grabbed properly", {
+  expect_identical(grab_names(df,dplyr::starts_with("ca")),
+                   subset(names(df),startsWith(names(df), "ca"))
+                   )
+})