diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index ebf4f77..648f7a8 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -30,7 +30,7 @@ jobs:
 
     - name: Install
       run: |
-        pip install --upgrade pytest codecov pytest-cov
+        pip install --upgrade pytest codecov pytest-cov h5py
         pip install .[test,cwl,parsl]
 
     - name: Tests
diff --git a/ceci/stage.py b/ceci/stage.py
index a292c80..9dfa7e0 100644
--- a/ceci/stage.py
+++ b/ceci/stage.py
@@ -448,13 +448,13 @@ def split_tasks_by_rank(self, tasks):
         ----------
         tasks: iterable
             Tasks to split up
-        
+
         """
         for i, task in enumerate(tasks):
             if i % self.size == self.rank:
                 yield task
 
-    def data_ranges_by_rank(self, n_rows, chunk_rows):
+    def data_ranges_by_rank(self, n_rows, chunk_rows, parallel=True):
         """Split a number of rows by process.
 
         Given a total number of rows to read and a chunk size, yield
@@ -471,7 +471,11 @@ def data_ranges_by_rank(self, n_rows, chunk_rows):
         n_chunks = n_rows // chunk_rows
         if n_chunks * chunk_rows < n_rows:
             n_chunks += 1
-        for i in self.split_tasks_by_rank(range(n_chunks)):
+        if parallel:
+            it = self.split_tasks_by_rank(range(n_chunks))
+        else:
+            it = range(n_chunks)
+        for i in it:
             start = i * chunk_rows
             end = min((i + 1) * chunk_rows, n_rows)
             yield start, end
@@ -721,7 +725,7 @@ def read_config(self, args):
 
         return my_config
 
-    def iterate_fits(self, tag, hdunum, cols, chunk_rows):
+    def iterate_fits(self, tag, hdunum, cols, chunk_rows, parallel=True):
         """
         Loop through chunks of the input data from a FITS file with the given tag
 
@@ -730,11 +734,11 @@ def iterate_fits(self, tag, hdunum, cols, chunk_rows):
         fits = self.open_input(tag)
         ext = fits[hdunum]
         n = ext.get_nrows()
-        for start, end in self.data_ranges_by_rank(n, chunk_rows):
+        for start, end in self.data_ranges_by_rank(n, chunk_rows, parallel=True):
             data = ext.read_columns(cols, rows=range(start, end))
             yield start, end, data
 
-    def iterate_hdf(self, tag, group_name, cols, chunk_rows):
+    def iterate_hdf(self, tag, group_name, cols, chunk_rows, parallel=True):
         """
         Loop through chunks of the input data from an HDF5 file with the given tag.
 
@@ -757,7 +761,7 @@ def iterate_hdf(self, tag, group_name, cols, chunk_rows):
             )
 
         # Iterate through the data providing chunks
-        for start, end in self.data_ranges_by_rank(n, chunk_rows):
+        for start, end in self.data_ranges_by_rank(n, chunk_rows, parallel=parallel):
             data = {col: group[col][start:end] for col in cols}
             yield start, end, data
 
diff --git a/ceci_example/types.py b/ceci_example/types.py
index 40d6dcd..c5e4e1a 100644
--- a/ceci_example/types.py
+++ b/ceci_example/types.py
@@ -16,6 +16,15 @@ class DataFile:
 
     """
 
+    def __init__(self, path, mode, extra_provenance=None, validate=True, **kwargs):
+        self.path = path
+        self.mode = mode
+
+        if mode not in ["r", "w"]:
+            raise ValueError(f"File 'mode' argument must be 'r' or 'w' not '{mode}'")
+
+        self.file = self.open(path, mode, **kwargs)
+
     @classmethod
     def open(cls, path, mode):
         """
diff --git a/tests/test_stage.py b/tests/test_stage.py
index 552575c..6a675f8 100644
--- a/tests/test_stage.py
+++ b/tests/test_stage.py
@@ -1,5 +1,7 @@
 from ceci.stage import PipelineStage
+from ceci_example.types import HDFFile
 import pytest
+import numpy as np
 
 # TODO: test MPI facilities properly with:
 # https://github.com/rmjarvis/TreeCorr/blob/releases/4.1/tests/mock_mpi.py
@@ -26,14 +28,14 @@ class TestStage(PipelineStage):
     # This one should work
     class TestStage(PipelineStage):
         name = "test"
-        inputs = []
+        inputs = [("inp1", HDFFile)]
         outputs = []
         config = {}
 
     assert PipelineStage.get_stage("test") == TestStage
     assert TestStage.get_module().endswith("test_stage")
 
-    s = TestStage({"config": "tests/config.yml"})
+    s = TestStage({"config": "tests/config.yml", "inp1": "tests/test.hdf5"})
 
     assert s.rank == 0
     assert s.size == 1
@@ -45,9 +47,15 @@ class TestStage(PipelineStage):
     assert r[0] == (0, 100)
     assert r[2] == (200, 300)
 
+    r = list(s.iterate_hdf("inp1", "group1", ["x", "y", "z"], 10))
+    for ri in r:
+        s, e, ri = ri
+        assert len(ri["x"] == 10)
+    assert np.all(r[4][2]["z"] == [-80, -82, -84, -86, -88, -90, -92, -94, -96, -98])
+
     # Fake that we are processor 4/10
     comm = MockCommunicator(10, 4)
-    s = TestStage({"config": "tests/config.yml"}, comm=comm)
+    s = TestStage({"config": "tests/config.yml", "inp1": "tests/test.hdf5"}, comm=comm)
 
     assert s.rank == 4
     assert s.size == 10
@@ -59,6 +67,19 @@ class TestStage(PipelineStage):
     assert r[0] == (400, 500)
     assert r[3] == (3400, 3500)
 
+    r = list(s.iterate_hdf("inp1", "group1", ["x", "y", "z"], 10))
+    assert len(r) == 1
+    st, e, r = r[0]
+    assert st == 40
+    assert e == 50
+    assert np.all(r["x"] == range(40, 50))
+
+    r = list(s.iterate_hdf("inp1", "group1", ["x", "y", "z"], 10, parallel=False))
+    for ri in r:
+        s, e, ri = ri
+        assert len(ri["x"] == 10)
+    assert np.all(r[4][2]["z"] == [-80, -82, -84, -86, -88, -90, -92, -94, -96, -98])
+
     # I'd rather not attempt to unit test MPI stuff - that sounds very unreliable