diff --git a/tests/test_absolutize.py b/tests/test_absolutize.py
index 37dbac9..ad0ac91 100644
--- a/tests/test_absolutize.py
+++ b/tests/test_absolutize.py
@@ -10,8 +10,8 @@
 from workflowhub_graph.merge import merge_all_files
 
 
-def get_test_data_file(filename):
-    """Returns the path to a test data file."""
+def get_test_data_file(filename=""):
+    """Returns the path to a test data file given it's relative path."""
 
     tests_dir = os.path.dirname(os.path.abspath(__file__))
     return os.path.join(tests_dir, "test_data", filename)
@@ -19,9 +19,9 @@ def get_test_data_file(filename):
 
 class TestAbsolutizePaths:  # (unittest.TestCase):
     # NOTE: ids can not be found, like 634, or forbidden, like 678
-    @pytest.mark.parametrize("workflow_id", [41, 552])
+    @pytest.mark.parametrize("workflow_id", [41, 552, 883])
     def test_make_paths_absolute(self, workflow_id):
-        with patch_rdflib_urlopen(get_test_data_file):
+        with patch_rdflib_urlopen(get_test_data_file(), write_cache=False):
             with open(
                 get_test_data_file(f"{workflow_id}_ro-crate-metadata.json"), "r"
             ) as f:
@@ -40,11 +40,13 @@ def test_make_paths_absolute(self, workflow_id):
             assert is_all_absolute(G)
 
     def test_merged(self):
-        # G = merge_all_files(get_test_data_file("[0-9]*ro-crate*.json"))
-        G = merge_all_files("data/[0-9]*ro-crate*.json")
-        assert is_all_absolute(G)
+        G = merge_all_files(
+            get_test_data_file("[0-9]*ro-crate*.json"),
+            cache_base_dir=get_test_data_file(),
+            write_cache=False,
+        )
 
-        print(list(G.triples((None, None, None))))
+        assert is_all_absolute(G)
 
         for s, o in G.subject_objects(rdflib.URIRef("http://schema.org/author")):
             print(s, o)
diff --git a/tests/test_data/883_ro-crate-metadata.json b/tests/test_data/883_ro-crate-metadata.json
new file mode 100644
index 0000000..b8320f9
--- /dev/null
+++ b/tests/test_data/883_ro-crate-metadata.json
@@ -0,0 +1,68 @@
+{
+  "@context": [
+    "https://w3id.org/ro/crate/1.1/context"
+  ],
+  "@graph": [
+    {
+      "@id": "ro-crate-metadata.json",
+      "@type": "CreativeWork",
+      "about": {
+        "@id": "https://training.galaxyproject.org/training-material/topics/introduction/tutorials/galaxy-intro-101-everyone/workflows#main_workflow.ga"
+      },
+      "conformsTo": {
+        "@id": "https://w3id.org/ro/crate/1.1"
+      }
+    },
+    {
+      "@id": "ro-crate-preview.html",
+      "@type": "CreativeWork",
+      "about": {
+        "@id": "./"
+      }
+    },
+    {
+      "@id": "https://training.galaxyproject.org/training-material/topics/introduction/tutorials/galaxy-intro-101-everyone/workflows#main_workflow.ga",
+      "@type": "Dataset",
+      "name": "GTN Training: Galaxy 101 For Everyone",
+      "description": "Galaxy workflow",
+      "version": "16",
+      "license": "https://spdx.org/licenses/CC-BY-4.0",
+      "datePublished": "2024-03-18T12:38:43.978+01:00",
+      "mainEntity": {
+        "@id": "main_workflow.ga"
+      },
+      "hasPart": [
+        {
+          "@id": "main_workflow.ga"
+        }
+      ]
+    },
+    {
+      "@id": "main_workflow.ga",
+      "@type": [
+        "File",
+        "SoftwareSourceCode",
+        "ComputationalWorkflow"
+      ],
+      "author": [
+
+      ],
+      "name": "GTN Training: Galaxy 101 For Everyone",
+      "programmingLanguage": {
+        "@id": "https://w3id.org/workflowhub/workflow-ro-crate#galaxy"
+      }
+    },
+    {
+      "@id": "https://w3id.org/workflowhub/workflow-ro-crate#galaxy",
+      "@type": "ComputerLanguage",
+      "identifier": {
+        "@id": "https://galaxyproject.org/"
+      },
+      "name": "Galaxy",
+      "url": {
+        "@id": "https://galaxyproject.org/"
+      },
+      "version": "23.1"
+    }
+  ]
+}
\ No newline at end of file
diff --git a/tests/test_data/ro-crate-context-1.0.json b/tests/test_data/w3id-org-ro-crate-1-0-context
similarity index 100%
rename from tests/test_data/ro-crate-context-1.0.json
rename to tests/test_data/w3id-org-ro-crate-1-0-context
diff --git a/tests/test_data/ro-crate-context-1.1.json b/tests/test_data/w3id-org-ro-crate-1-1-context
similarity index 100%
rename from tests/test_data/ro-crate-context-1.1.json
rename to tests/test_data/w3id-org-ro-crate-1-1-context
diff --git a/workflowhub_graph/cachedurlopen.py b/workflowhub_graph/cachedurlopen.py
index 9475e6c..9dd8269 100644
--- a/workflowhub_graph/cachedurlopen.py
+++ b/workflowhub_graph/cachedurlopen.py
@@ -1,22 +1,38 @@
+import os
+import re
 from unittest.mock import patch, MagicMock
 from contextlib import contextmanager
 import io
+from urllib.parse import urlparse
+from urllib.request import urlopen
 
 
-cached_urls = {
-    "https://w3id.org/ro/crate/1.0/context": "ro-crate-context-1.0.json",
-    "https://w3id.org/ro/crate/1.1/context": "ro-crate-context-1.1.json",
-}
+def url_to_filename(url):
+    parsed = urlparse(url)
+    if parsed.scheme not in ["http", "https"]:
+        raise ValueError(f"Unsupported scheme {parsed.scheme}")
+
+    return re.sub("[^0-9a-z]+", "-", (parsed.netloc + parsed.path).lower().strip("_"))
 
 
 @contextmanager
-def patch_rdflib_urlopen(file_locator):
+def patch_rdflib_urlopen(
+    cache_base_dir=None,
+    write_cache=True,
+    allowed_urls_pattern=r"https://w3id.org/ro/crate/1\.[01]/context",
+):
+    allowed_urls_re = re.compile(allowed_urls_pattern)
+    if cache_base_dir is None:
+        cache_base_dir = "cached_urlopen"
+        os.makedirs(cache_base_dir, exist_ok=True)
+
     def cached_urlopen(request):
         url = request.get_full_url()
 
-        if url not in cached_urls:
-            # TODO: store and use cache
-            raise ValueError(f"URL {url} not in cache, have: {cached_urls.keys()}")
+        if not allowed_urls_re.match(url):
+            raise ValueError(
+                f"URL {url} not allowed to cache, allowed: {allowed_urls_pattern}"
+            )
 
         class Response(io.StringIO):
             content_type = "text/html"
@@ -28,7 +44,21 @@ def info(self):
             def geturl(self):
                 return url
 
-        content = open(file_locator(cached_urls[url]), "rt").read()
+        cached_filename = os.path.join(cache_base_dir, url_to_filename(url))
+
+        if not os.path.exists(cached_filename):
+            if write_cache:
+                response = urlopen(request)
+                content = response.read().decode("utf-8")
+
+                with open(cached_filename, "wt") as f:
+                    f.write(content)
+            else:
+                raise ValueError(
+                    f"Cache file {cached_filename} not found, not allowed to download and update cache"
+                )
+
+        content = open(cached_filename, "rt").read()
 
         return Response(content)
 
diff --git a/workflowhub_graph/merge.py b/workflowhub_graph/merge.py
index 5008386..dba6286 100644
--- a/workflowhub_graph/merge.py
+++ b/workflowhub_graph/merge.py
@@ -10,7 +10,7 @@
 from workflowhub_graph.constants import BASE_URL
 
 
-def merge_all_files(pattern="data/*.json") -> rdflib.Graph:
+def merge_all_files(pattern="data/*.json", **cache_kwargs) -> rdflib.Graph:
     G = rdflib.Graph()
 
     filenames = glob.glob(pattern)
@@ -27,10 +27,7 @@ def merge_all_files(pattern="data/*.json") -> rdflib.Graph:
             w_id = int(os.path.basename(fn).split("_")[0])
             json_data = make_paths_absolute(json_data, BASE_URL, w_id)
 
-            # TODO: make this actual caching, and pre-populate in the test
-            with patch_rdflib_urlopen(
-                lambda x: "tests/test_data/ro-crate-context-1.0.json"
-            ):
+            with patch_rdflib_urlopen(**cache_kwargs):
                 G.parse(data=json_data, format="json-ld")
 
     # TODO: set a total version
@@ -49,4 +46,4 @@ def main():
 
 
 if __name__ == "__main__":
-    main()
\ No newline at end of file
+    main()