Add tests for csv parsing empty data

Author: amas0

test/test_sample.py

@@ -2138,3 +2138,13 @@ def test_sample_dense_mass_matrix():
     fit = linear_model.sample(data=jdata, metric="dense_e", chains=2)
     assert fit.metric is not None
     assert fit.metric.shape == (2, 3, 3)
+
+
+def test_no_output_draws():
+    stan = os.path.join(DATAFILES_PATH, 'bernoulli.stan')
+    model = cmdstanpy.CmdStanModel(stan_file=stan)
+    data = os.path.join(DATAFILES_PATH, 'bernoulli.data.json')
+
+    mcmc = model.sample(data=data, iter_sampling=0, save_warmup=False, chains=2)
+    draws = mcmc.draws()
+    assert np.array_equal(draws, np.empty((0, 2, len(mcmc.column_names))))

test/test_stancsv.py

@@ -136,17 +136,10 @@ def test_csv_bytes_to_numpy_with_header_no_polars():
         assert np.array_equal(arr_out, expected)
 
 
-def test_csv_bytes_to_numpy_empty():
-    lines = [b""]
-    with pytest.raises(ValueError):
-        stancsv.csv_bytes_list_to_numpy(lines)
-
-
-def test_csv_bytes_to_numpy_empty_no_polars():
-    lines = [b""]
-    with without_import("polars", cmdstanpy.utils.stancsv):
-        with pytest.raises(ValueError):
-            stancsv.csv_bytes_list_to_numpy(lines)
+def test_csv_bytes_empty():
+    lines = []
+    arr = stancsv.csv_bytes_list_to_numpy(lines)
+    assert np.array_equal(arr, np.empty((0,)))
 
 
 def test_csv_bytes_to_numpy_header_no_draws():
@@ -156,8 +149,8 @@ def test_csv_bytes_to_numpy_header_no_draws():
             b"n_leapfrog__,divergent__,energy__,theta\n"
         ),
     ]
-    with pytest.raises(ValueError):
-        stancsv.csv_bytes_list_to_numpy(lines)
+    arr = stancsv.csv_bytes_list_to_numpy(lines)
+    assert arr.shape == (0, 8)
 
 
 def test_csv_bytes_to_numpy_header_no_draws_no_polars():
@@ -167,9 +160,8 @@ def test_csv_bytes_to_numpy_header_no_draws_no_polars():
             b"n_leapfrog__,divergent__,energy__,theta\n"
         ),
     ]
-    with without_import("polars", cmdstanpy.utils.stancsv):
-        with pytest.raises(ValueError):
-            stancsv.csv_bytes_list_to_numpy(lines)
+    arr = stancsv.csv_bytes_list_to_numpy(lines)
+    assert arr.shape == (0, 8)
 
 
 def test_parse_comments_and_draws():