log_file_name in tune.run() (#681)

* log_file_name in tune.run()

* use_ray validates log_file_name

* assert no ray_args when not use_ray

* import os and use os.path

test/tune/test_constraints.py

@@ -22,6 +22,7 @@ def test_config_constraint():
         metric="metric",
         mode="max",
         num_samples=100,
+        log_file_name="logs/config_constraint.log",
     )
 
     assert analysis.best_config["x"] > analysis.best_config["y"]

test/tune/test_searcher.py

@@ -295,7 +295,7 @@ def test_searcher():
     print(searcher.suggest("t1"))
     from flaml import tune
 
-    tune.run(lambda x: 1, config={}, use_ray=use_ray)
+    tune.run(lambda x: 1, config={}, use_ray=use_ray, log_file_name="logs/searcher.log")
 
 
 def test_no_optuna():

test/tune/test_tune.py

@@ -47,6 +47,8 @@ def test_nested_run():
         mode="min",
         num_samples=5,
         local_dir="logs",
+        log_file_name="logs/nested.log",
+        verbose=3,
     )
     print(analysis.best_result)