diff --git a/tests/testthat/test_dockerize.R b/tests/testthat/test_dockerize.R
index c715b5d..c9c70a6 100644
--- a/tests/testthat/test_dockerize.R
+++ b/tests/testthat/test_dockerize.R
@@ -1,3 +1,7 @@
+.gen_temp_dir <- function() {
+    file.path(tempdir(), paste(sample(c(LETTERS, letters), 20, replace = TRUE), collapse = ""))
+}
+
 test_that("defensive programming", {
     graph <- readRDS("../testdata/sle_graph.RDS")
     expect_error(dockerize(graph, output_dir = tempdir()))
@@ -5,7 +9,7 @@ test_that("defensive programming", {
 
 test_that("integration of #13 in dockerize()", {
     gran_ok <- readRDS("../testdata/gran_ok.RDS")
-    temp_dir <- file.path(tempdir(), sample(1:10000, size = 1))
+    temp_dir <- .gen_temp_dir()
     dockerize(granlist = gran_ok, output_dir = temp_dir) ## granlist_as_comment = TRUE
     x <- readLines(file.path(temp_dir, "gran.R"))
     expect_true(any(grepl("^## ## To reconstruct this file", x)))
@@ -17,7 +21,7 @@ test_that("integration of #13 in dockerize()", {
 test_that("integration of #16 in dockerize()", {
     ## verbose
     gran_ok <- readRDS("../testdata/gran_ok.RDS")
-    temp_dir <- file.path(tempdir(), sample(1:10000, size = 1))
+    temp_dir <- .gen_temp_dir()
     dockerize(granlist = gran_ok, output_dir = temp_dir) ## verbose = TRUE
     x <- readLines(file.path(temp_dir, "gran.R"))
     expect_true(any(grepl("^verbose <- TRUE", x)))
@@ -39,7 +43,7 @@ test_that("integration of #16 in dockerize()", {
 
 test_that("integration of #18 in dockerize()", {
     gran_ok <- readRDS("../testdata/gran_ok.RDS")
-    temp_dir <- file.path(tempdir(), sample(1:10000, size = 1))
+    temp_dir <- .gen_temp_dir()
     dockerize(granlist = gran_ok, output_dir = temp_dir) ## cran_mirror = "https://cran.r-project.org/"
     x <- readLines(file.path(temp_dir, "gran.R"))
     expect_true(any(grepl("^cran_mirror <- \"https://cran\\.r\\-project\\.org/\"", x)))
@@ -58,7 +62,7 @@ test_that("integration of #18 in dockerize()", {
 test_that("integration of #20 to dockerize()", {
     gran_ok <- readRDS("../testdata/gran_ok.RDS")
     expect_equal(gran_ok$r_version, "4.2.2")
-    temp_dir <- file.path(tempdir(), sample(1:10000, size = 1))
+    temp_dir <- .gen_temp_dir()
     dockerize(gran_ok, output_dir = temp_dir) ## cran_mirror = "https://cran.r-project.org/"
     x <- readLines(file.path(temp_dir, "gran.R"))
     expect_true(any(grepl("^cran_mirror <- \"https://cran\\.r\\-project\\.org/\"", x)))
@@ -78,7 +82,7 @@ test_that("integration of #20 to dockerize()", {
 test_that("Dockerize R < 3.1 and >= 2.1", {
     gran_rio <- readRDS("../testdata/gran_rio_old.RDS")
     expect_equal(gran_rio$r_version, "3.0.1")
-    temp_dir <- file.path(tempdir(), sample(1:10000, size = 1))
+    temp_dir <- .gen_temp_dir()
     dockerize(gran_rio, output_dir = temp_dir)
     expect_true(file.exists(file.path(temp_dir, "compile_r.sh")))
     Dockerfile <- readLines(file.path(temp_dir, "Dockerfile"))
@@ -92,7 +96,7 @@ test_that("Dockerize R < 3.1 and >= 2.1", {
 test_that("Docker R < 2.1", {
     gran_rio <- readRDS("../testdata/gran_rio_old.RDS")
     gran_rio$r_version <- "2.1.0" ## exactly 2.1.0, no error
-    temp_dir <- file.path(tempdir(), sample(1:10000, size = 1))
+    temp_dir <- .gen_temp_dir()
     expect_error(dockerize(gran_rio, output_dir = temp_dir), NA)
     gran_rio <- readRDS("../testdata/gran_rio_old.RDS")
     gran_rio$r_version <- "2.0.0"
@@ -115,6 +119,7 @@ test_that(".consolidate_sysreqs and issue #21", {
 
 test_that("Dockerize warning, issue #21", {
     graph <- readRDS("../testdata/issue21.RDS")
-    temp_dir <- file.path(tempdir(), sample(1:10000, size = 1))
+    temp_dir <- .gen_temp_dir()
     expect_warning(dockerize(graph, output_dir = temp_dir))
 })
+
diff --git a/tests/testthat/test_resolve.R b/tests/testthat/test_resolve.R
index c25c452..61278ad 100644
--- a/tests/testthat/test_resolve.R
+++ b/tests/testthat/test_resolve.R
@@ -1,3 +1,7 @@
+.gen_temp_dir <- function() {
+    file.path(tempdir(), paste(sample(c(LETTERS, letters), 20, replace = TRUE), collapse = ""))
+}
+
 test_that("defensive programming", {
     expect_error(resolve("LDAvis", os = "windows"))
 })
@@ -48,7 +52,7 @@ test_that("cache #17", {
     skip_if_offline()
     skip_on_cran()
     gran_ok <- readRDS("../testdata/gran_ok.RDS")
-    temp_dir <- file.path(tempdir(), sample(1:10000, size = 1))
+    temp_dir <- .gen_temp_dir()
     dockerize(gran_ok, output_dir = temp_dir) ## cache = FALSE
     x <- readLines(file.path(temp_dir, "Dockerfile"))
     expect_false(any(grepl("^COPY cache", x)))
@@ -71,7 +75,7 @@ test_that("cache for R < 3.1 and R >= 2.1", {
     skip_on_cran()
     gran_rio <- readRDS("../testdata/gran_rio_old.RDS")
     expect_equal(gran_rio$r_version, "3.0.1")
-    temp_dir <- file.path(tempdir(), sample(1:10000, size = 1))
+    temp_dir <- .gen_temp_dir()
     dockerize(gran_rio, output_dir = temp_dir, cache = TRUE, verbose = FALSE)
     x <- readLines(file.path(temp_dir, "Dockerfile"))
     expect_true(any(grepl("^COPY cache", x)))