[tune] Fix get_best_logdir behaviour (#5429)

* Fix get_best_logdir behaviour

* addtest

python/ray/tune/analysis/experiment_analysis.py

@@ -75,7 +75,7 @@ class Analysis(object):
             mode (str): One of [min, max].
 
         """
-        df = self.dataframe()
+        df = self.dataframe(metric=metric, mode=mode)
         if mode == "max":
             return df.iloc[df[metric].idxmax()].logdir
         elif mode == "min":

python/ray/tune/tests/test_experiment_analysis.py

@@ -141,6 +141,13 @@ class AnalysisSuite(unittest.TestCase):
         self.assertTrue(logdir2.startswith(self.test_dir))
         self.assertNotEquals(logdir, logdir2)
 
+    def testBestConfigIsLogdir(self):
+        analysis = Analysis(self.test_dir)
+        for metric, mode in [(self.metric, "min"), (self.metric, "max")]:
+            logdir = analysis.get_best_logdir(metric, mode=mode)
+            best_config = analysis.get_best_config(metric, mode=mode)
+            self.assertEquals(analysis.get_all_configs()[logdir], best_config)
+
 
 if __name__ == "__main__":
     unittest.main(verbosity=2)