test: Explicitly specify directory where to search tests for

This change allows `test_runner.py` to work from an out-of-source build
directory using a symlink, a hard link or a copy on any platform.

test/functional/test_runner.py

@@ -528,6 +528,12 @@ def run_tests(*, test_list, src_dir, build_dir, tmpdir, jobs=1, enable_coverage=
 
     # Test Framework Tests
     print("Running Unit Tests for Test Framework Modules")
+
+    tests_dir = src_dir + '/test/functional/'
+    # This allows `test_runner.py` to work from an out-of-source build directory using a symlink,
+    # a hard link or a copy on any platform. See https://github.com/bitcoin/bitcoin/pull/27561.
+    sys.path.append(tests_dir)
+
     test_framework_tests = unittest.TestSuite()
     for module in TEST_FRAMEWORK_MODULES:
         test_framework_tests.addTest(unittest.TestLoader().loadTestsFromName("test_framework.{}".format(module)))
@@ -536,8 +542,6 @@ def run_tests(*, test_list, src_dir, build_dir, tmpdir, jobs=1, enable_coverage=
         logging.debug("Early exiting after failure in TestFramework unit tests")
         sys.exit(False)
 
-    tests_dir = src_dir + '/test/functional/'
-
     flags = ['--cachedir={}'.format(cache_dir)] + args
 
     if enable_coverage: