While I worked on the previous commit, I noticed that there is a room
to improve descriptions about TEST_DEVS. Add more descriptions about it
in Documentation/running-tests.md. Also note the relation between
TEST_DEVS and the test_device() function in the 'new' script.

This reverts commit 6aa89879d4b8a79a54589b53fe287fd188ca2131.
---
 Documentation/running-tests.md | 13 ++++++++-----
 new                            |  3 ++-
 2 files changed, 10 insertions(+), 6 deletions(-)

diff --git a/Documentation/running-tests.md b/Documentation/running-tests.md
index f037634..8ccd739 100644
--- a/Documentation/running-tests.md
+++ b/Documentation/running-tests.md
@@ -30,17 +30,20 @@ options have precedence over the configuration file.
 
 ### Test Devices
 
-The `TEST_DEVS` variable is an array of block devices to test on. Tests will be
-run on all of these devices where applicable. Note that tests are destructive
-and will overwrite any data on these devices.
+Some test cases require a block device for testing. These test cases implement
+a special test function test_device(). The `TEST_DEVS` variable is an array of
+block devices that such test cases to test on. Every test will be run on each of
+these devices where applicable. Note that tests are destructive and will
+overwrite any data on these devices.
 
 ```sh
 TEST_DEVS=(/dev/nvme0n1 /dev/sdb)
 ```
 
 If `TEST_DEVS` is not defined or is empty, only tests which do not require a
-device will be run. If `TEST_DEVS` is defined as a normal variable instead of
-an array, it will be converted to an array by splitting on whitespace.
+device will be run, which implments the test function 'test()'. If `TEST_DEVS`
+is defined as a normal variable instead of an array, it will be converted to an
+array by splitting on whitespace.
 
 Some test cases require multiple block devices for single test run. These test
 cases implement a special test function test_device_array(). TEST_CASE_DEV_ARRAY
diff --git a/new b/new
index df4092c..4773175 100755
--- a/new
+++ b/new
@@ -235,7 +235,8 @@ DESCRIPTION=""
 #
 # Tests that require a test device should rename test() to test_device(). These
 # tests will be run with a few more variables defined:
-#    - \$TEST_DEV -- the block device to run the test on (e.g., /dev/sda1).
+#    - \$TEST_DEV -- the block device to run the test on (e.g., /dev/sda1). The
+#                    device is taken from TEST_DEVS in the config for each run.
 #    - \$TEST_DEV_SYSFS -- the sysfs directory of the device (e.g.,
 #                         /sys/block/sda). In general, you should use the
 #                         _test_dev_queue_{get,set} helpers. If the device is a
-- 
2.51.0