From da9e3eec651797301a41f7a7ab5f47241b69dece Mon Sep 17 00:00:00 2001
From: John Bytheway <jbytheway@gmail.com>
Date: Fri, 10 Apr 2020 17:25:13 -0400
Subject: [PATCH] Add test for consistent random ordering

---
 projects/CMakeLists.txt                 |  2 +
 projects/TestScripts/testRandomOrder.py | 53 +++++++++++++++++++++++++
 2 files changed, 55 insertions(+)
 create mode 100755 projects/TestScripts/testRandomOrder.py

diff --git a/projects/CMakeLists.txt b/projects/CMakeLists.txt
index 0aafc1780d..08badb809a 100644
--- a/projects/CMakeLists.txt
+++ b/projects/CMakeLists.txt
@@ -451,6 +451,8 @@ set_tests_properties(TestsInFile::InvalidTestNames-1 PROPERTIES PASS_REGULAR_EXP
 add_test(NAME TestsInFile::InvalidTestNames-2 COMMAND $<TARGET_FILE:SelfTest> "-f ${CATCH_DIR}/projects/SelfTest/Misc/invalid-test-names.input")
 set_tests_properties(TestsInFile::InvalidTestNames-2 PROPERTIES PASS_REGULAR_EXPRESSION "No tests ran")
 
+add_test(NAME RandomTestOrdering COMMAND ${PYTHON_EXECUTABLE}
+  ${CATCH_DIR}/projects/TestScripts/testRandomOrder.py $<TARGET_FILE:SelfTest>)
 
 if (CATCH_USE_VALGRIND)
     add_test(NAME ValgrindRunTests COMMAND valgrind --leak-check=full --error-exitcode=1 $<TARGET_FILE:SelfTest>)
diff --git a/projects/TestScripts/testRandomOrder.py b/projects/TestScripts/testRandomOrder.py
new file mode 100755
index 0000000000..68f53f19af
--- /dev/null
+++ b/projects/TestScripts/testRandomOrder.py
@@ -0,0 +1,53 @@
+#!/usr/bin/env python3
+
+import subprocess
+import sys
+
+def list_tests(self_test_exe, tags, rng_seed):
+    cmd = [self_test_exe, '--list-test-names-only', '--order', 'rand',
+            '--rng-seed', str(rng_seed)]
+    tags_arg = ','.join('[{}]'.format(t) for t in tags)
+    if tags_arg:
+        cmd.append(tags_arg + '~[.]')
+    process = subprocess.Popen(
+            cmd, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
+    stdout, stderr = process.communicate()
+    if stderr:
+        raise RuntimeError("Unexpected error output:\n" + process.stderr)
+    result = stdout.split(b'\n')
+    result = [s for s in result if s]
+    if len(result) < 2:
+        raise RuntimeError("Unexpectedly few tests listed (got {})".format(
+            len(result)))
+    return result
+
+def check_is_sublist_of(shorter, longer):
+    assert len(shorter) < len(longer)
+    assert len(set(longer)) == len(longer)
+
+    indexes_in_longer = {s: i for i, s in enumerate(longer)}
+    for s1, s2 in zip(shorter, shorter[1:]):
+        assert indexes_in_longer[s1] < indexes_in_longer[s2], (
+                '{} comes before {} in longer list.\n'
+                'Longer: {}\nShorter: {}'.format(s2, s1, longer, shorter))
+
+def main():
+    self_test_exe, = sys.argv[1:]
+
+    list_one_tag = list_tests(self_test_exe, ['generators'], 1)
+    list_two_tags = list_tests(self_test_exe, ['generators', 'matchers'], 1)
+    list_all = list_tests(self_test_exe, [], 1)
+
+    # First, verify that restricting to a subset yields the same order
+    check_is_sublist_of(list_two_tags, list_all)
+    check_is_sublist_of(list_one_tag, list_two_tags)
+
+    # Second, verify that different seeds yield different orders
+    num_seeds = 100
+    seeds = range(1, num_seeds + 1) # Avoid zero since that's special
+    lists = {tuple(list_tests(self_test_exe, [], seed)) for seed in seeds}
+    assert len(lists) == num_seeds, (
+            'Got {} distict lists from {} seeds'.format(len(lists), num_seeds))
+
+if __name__ == '__main__':
+    sys.exit(main())