Add unit test for dump_config auto format detection

Author: tskisner

src/toast/config/cli.py

@@ -100,11 +100,11 @@ def dump_config(file, conf, format=None, comm=None):
     if format is None:
         # Guess from the file name
         base, ext = os.path.splitext(file)
-        if ext == "toml":
+        if ext == ".toml":
             format = "toml"
-        elif ext == "json" or ext == "jsn":
+        elif ext == ".json" or ext == ".jsn":
             format = "json"
-        elif ext == "yaml" or ext == "yml":
+        elif ext == ".yaml" or ext == ".yml":
             format = "yaml"
         else:
             msg = "Cannot determine format (yaml, toml, json) from"

src/toast/tests/config.py

@@ -451,6 +451,19 @@ def test_config_multi(self):
             if self.toastcomm.comm_world is not None:
                 self.toastcomm.comm_world.barrier()
 
+            conf_defaults_auto_file = os.path.join(
+                self.outdir, f"multi_defaults_auto.{case}"
+            )
+            if self.toastcomm.world_rank == 0:
+                dump_config(
+                    conf_defaults_auto_file,
+                    defaults,
+                    format=None,
+                    comm=self.toastcomm.comm_world,
+                )
+            if self.toastcomm.comm_world is not None:
+                self.toastcomm.comm_world.barrier()
+
             # Now change some values
             testops["mem_count"].prefix = "newpref"
             testops["mem_count"].enabled = False