diff --git a/.gitignore b/.gitignore
index 9b164c65..1ddbbd42 100644
--- a/.gitignore
+++ b/.gitignore
@@ -6,6 +6,7 @@
 docs/api/
 tests/data/MOP*.he5
 tests/data/TROPOMI*.nc
+tests/data/OMPS-*.h5
 
 # Default GitHub .gitignore for Python below:
 
diff --git a/tests/test_omps_l3.py b/tests/test_omps_l3.py
index 2d3b3520..00be2ed3 100644
--- a/tests/test_omps_l3.py
+++ b/tests/test_omps_l3.py
@@ -1,12 +1,67 @@
+import shutil
+import warnings
 from pathlib import Path
 
 import pandas as pd
+import pytest
+from filelock import FileLock
 
 from monetio.sat._omps_l3_mm import open_dataset
 
+HERE = Path(__file__).parent
 
-def test_open_dataset():
-    ps = sorted(Path("~/Downloads/").expanduser().glob("OMPS-TO3-L3-DAILY_v2.1_*.h5"))
+FNS = [
+    "OMPS-TO3-L3-DAILY_v2.1_20190905.h5",
+    "OMPS-TO3-L3-DAILY_v2.1_20190906.h5",
+]
+
+
+def retrieve_test_file(i):
+    fn = FNS[i]
+
+    # Download to tests/data if not already present
+    p = HERE / "data" / fn
+    if not p.is_file():
+        warnings.warn(f"Downloading test file {fn} for MOPITT L3 test")
+        import requests
+
+        r = requests.get(
+            "https://csl.noaa.gov/groups/csl4/modeldata/melodies-monet/data/"
+            f"example_observation_data/satellite/{fn}",
+            stream=True,
+        )
+        r.raise_for_status()
+        with open(p, "wb") as f:
+            f.write(r.content)
+
+    return p
+
+
+@pytest.fixture(scope="session")
+def test_file_paths(tmp_path_factory, worker_id):
+    if worker_id == "master":
+        # Not executing with multiple workers;
+        # let pytest's fixture caching do its job
+        return [retrieve_test_file(i) for i in range(len(FNS))]
+
+    # Get the temp directory shared by all workers
+    root_tmp_dir = tmp_path_factory.getbasetemp().parent
+
+    # Copy to the shared test location
+    p_tests = []
+    for i, p in enumerate(FNS):
+        p_test = root_tmp_dir / f"omps_l3_test_{i}.he5"
+        with FileLock(p_test.as_posix() + ".lock"):
+            if not p_test.is_file():
+                p = retrieve_test_file(i)
+                shutil.copy(p, p_test)
+            p_tests.append(p_test)
+
+    return p_tests
+
+
+def test_open_dataset(test_file_paths):
+    ps = test_file_paths
     ds = open_dataset(ps)
 
     assert ds.sizes["time"] == len(ps) == 2