add a script to run a single test

As a Meson developer it's often frustrating to have a single functional
test with a regression. These tests can be awkward to reproduce,
especially when they make use of a test.json file. This script provides
a simmple interface to call functional tests 1 at a time, regardless of
whether they use a test.json or not. If they do use a test.json, and
have a matrix, then the `--subtest` option can be used to select spcific
combinations, for example:
```sh
./run_single_test.py "test cases/frameworks/15 llvm" --subtest 1
```
will run only the second (zero indexed of course) subtest from the llvm
test cases.

This is not a super elegent script, but this is super useful.

1 files changed, 2 insertions, 1 deletions

diff --git a/run_tests.py b/run_tests.py
index 5a0a70c..1e01aa9 100755
--- a/run_tests.py
+++ b/run_tests.py
@@ -118,7 +118,8 @@ class FakeCompilerOptions:
     def __init__(self):
         self.value = []
 
-def get_fake_options(prefix=''):
+# TODO: use a typing.Protocol here
+def get_fake_options(prefix: str = '') -> argparse.Namespace:
     opts = argparse.Namespace()
     opts.native_file = []
     opts.cross_file = None