diff --git a/tests/run-tests.py b/tests/run-tests.py
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -35,6 +35,8 @@
 #      ./run-tests.py -j2 -c --local test-s*  # unsupported (and broken)
 #  9) parallel, custom tmp dir:
 #      ./run-tests.py -j2 --tmpdir /tmp/myhgtests
+#  10) parallel, pure, tests that call run-tests:
+#      ./run-tests.py --pure `grep -l run-tests.py *.t`
 #
 # (You could use any subset of the tests: test-s* happens to match
 # enough that it's worth doing parallel runs, few enough that it
diff --git a/tests/test-hghave.t b/tests/test-hghave.t
--- a/tests/test-hghave.t
+++ b/tests/test-hghave.t
@@ -18,7 +18,7 @@ Testing hghave extensibility for third p
   >   $ echo foo
   >   foo
   > EOF
-  $ run-tests.py test-hghaveaddon.t
+  $ run-tests.py $HGTEST_RUN_TESTS_PURE test-hghaveaddon.t
   .
   # Ran 1 tests, 0 skipped, 0 warned, 0 failed.
 
diff --git a/tests/test-run-tests.t b/tests/test-run-tests.t
--- a/tests/test-run-tests.t
+++ b/tests/test-run-tests.t
@@ -580,7 +580,7 @@ Mercurial source tree.
   >   $ echo foo
   >   foo
   > EOF
-  $ run-tests.py test-hghave.t
+  $ run-tests.py $HGTEST_RUN_TESTS_PURE test-hghave.t
   .
   # Ran 1 tests, 0 skipped, 0 warned, 0 failed.
 
@@ -599,7 +599,7 @@ running is placed.
   >   #
   >   # check-code - a style and portability checker for Mercurial
   > EOF
-  $ run-tests.py test-runtestdir.t
+  $ run-tests.py $HGTEST_RUN_TESTS_PURE test-runtestdir.t
   .
   # Ran 1 tests, 0 skipped, 0 warned, 0 failed.
 
@@ -616,7 +616,7 @@ test that TESTDIR is referred in PATH
   >   $ custom-command.sh
   >   hello world
   > EOF
-  $ run-tests.py test-testdir-path.t
+  $ run-tests.py $HGTEST_RUN_TESTS_PURE test-testdir-path.t
   .
   # Ran 1 tests, 0 skipped, 0 warned, 0 failed.
 
@@ -628,10 +628,10 @@ test support for --allow-slow-tests
   >   $ echo pass
   >   pass
   > EOF
-  $ run-tests.py test-very-slow-test.t
+  $ run-tests.py $HGTEST_RUN_TESTS_PURE test-very-slow-test.t
   s
   Skipped test-very-slow-test.t: skipped
   # Ran 0 tests, 1 skipped, 0 warned, 0 failed.
-  $ run-tests.py --allow-slow-tests test-very-slow-test.t
+  $ run-tests.py $HGTEST_RUN_TESTS_PURE --allow-slow-tests test-very-slow-test.t
   .
   # Ran 1 tests, 0 skipped, 0 warned, 0 failed.