add basic test for coverage

Author: valeriupredoi

tests/test_real_s3.py

@@ -11,7 +11,7 @@
 
 
 def test_anon_s3():
-    """Test a very basic but real S3 access."""
+    """Test a very basic but real S3 ANON access."""
     active_storage_url = "https://reductionist.jasmin.ac.uk/"  # Wacasoft
     bigger_file = "CMIP6-test.nc"  # tas; 15 (time) x 143 x 144 
 
@@ -36,13 +36,34 @@ def test_anon_s3():
         assert result == 197.69595    
 
 
-# this could be a slow test on GHA depending on network load
-# also Githb machines are very far from Oxford
+def test_s3_small_dataset():
+    """Run an S3 test on a small file."""
+    storage_options = {
+        'key': "f2d55c6dcfc7618b2c34e00b58df3cef",
+        'secret':
+        "$/'#M{0{/4rVhp%n^(XeX$q@y#&(NM3W1->~N.Q6VP.5[@bLpi='nt]AfH)>78pT",
+        'client_kwargs': {
+            'endpoint_url': "https://uor-aces-o.s3-ext.jc.rl.ac.uk"
+        },
+    }
+    active_storage_url = "https://reductionist.jasmin.ac.uk/"  # Wacasoft
+    bigger_file = "CMIP6-test.nc"  # tas; 15 (time) x 143 x 144
+
+    test_file_uri = os.path.join(S3_BUCKET, bigger_file)
+    print("S3 Test file path:", test_file_uri)
+    active = Active(test_file_uri,
+                    'tas',
+                    storage_options=storage_options,
+                    active_storage_url=active_storage_url)
+    active._version = 2
+    result = active.min()[0:3, 4:6, 7:9]
+    print("Result is", result)
+    assert result == 222.09129333496094
+
+
 @pytest.mark.slow
 def test_s3_dataset():
     """Run somewhat as the 'gold' test."""
-    # NOTE: "https://uor-aces-o.s3-ext.jc.rl.ac.uk" is the stable S3 JASMIN
-    # proxy that is now migrated to the new proxy (1 April 2025)
     storage_options = {
         'key': "f2d55c6dcfc7618b2c34e00b58df3cef",
         'secret':