diff --git a/tests/run-tests.py b/tests/run-tests.py
--- a/tests/run-tests.py
+++ b/tests/run-tests.py
@@ -2510,6 +2510,16 @@ class TestRunner(object):
             else:
                 args = os.listdir(b'.')
 
+        expanded_args = []
+        for arg in args:
+            if os.path.isdir(arg):
+                if not arg.endswith(b'/'):
+                    arg += b'/'
+                expanded_args.extend([arg + a for a in os.listdir(arg)])
+            else:
+                expanded_args.append(arg)
+        args = expanded_args
+
         tests = []
         for t in args:
             if not (os.path.basename(t).startswith(b'test-')
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
@@ -1261,6 +1261,24 @@ support for running a test outside the c
   .
   # Ran 1 tests, 0 skipped, 0 failed.
 
+support for automatically discovering test if arg is a folder
+  $ mkdir tmp && cd tmp
+
+  $ cat > test-uno.t << EOF
+  >   $ echo line
+  >   line
+  > EOF
+
+  $ cp test-uno.t test-dos.t
+  $ cd ..
+  $ cp -R tmp tmpp
+  $ cp tmp/test-uno.t test-solo.t
+
+  $ $PYTHON $TESTDIR/run-tests.py tmp/ test-solo.t tmpp
+  .....
+  # Ran 5 tests, 0 skipped, 0 failed.
+  $ rm -rf tmp tmpp
+
 support for running run-tests.py from another directory
   $ mkdir tmp && cd tmp
   $ cat > useful-file.sh << EOF