diff --git a/my/core/cfg.py b/my/core/cfg.py
index c8fa96e..344cfa9 100644
--- a/my/core/cfg.py
+++ b/my/core/cfg.py
@@ -16,3 +16,21 @@ def make_config(cls: Type[C], migration: Callable[[Attrs], Attrs]=lambda x: x) -
         if k in {f.name for f in fields(cls)}
     }
     return cls(**params) # type: ignore[call-arg]
+
+
+F = TypeVar('F')
+from contextlib import contextmanager
+import inspect
+from typing import Iterator
+@contextmanager
+def override_config(config: F) -> Iterator[F]:
+    '''
+    Temporary override for config's parameters, useful for testing/fake data/etc.
+    '''
+    orig_properties = {k: v for k, v in vars(config).items() if not k.startswith('__')}
+    try:
+        yield config
+    finally:
+        # ugh. __dict__ of type objects isn't writable..
+        for k, v in orig_properties.items():
+            setattr(config, k, v)
diff --git a/my/rescuetime.py b/my/rescuetime.py
index 4b46e2e..07abc8e 100644
--- a/my/rescuetime.py
+++ b/my/rescuetime.py
@@ -27,13 +27,13 @@ DAL = dal.DAL
 Entry = dal.Entry
 
 
-# todo needs to be cumulative cache
-@mcachew
-def entries(files=inputs()) -> Iterable[Entry]:
-    dal = DAL(files)
-    it = dal.iter_entries()
+@mcachew(hashf=lambda: inputs())
+def entries() -> Iterable[Entry]:
+    dal = DAL(inputs())
+    it = dal.entries()
     vit, eit = split_errors(it, ET=Exception)
     # todo handle errors, I guess initially I didn't because it's unclear how to easily group?
+    # todo would be nice if logger unwrapped causes by default??
     yield from vit
 
 
@@ -51,16 +51,31 @@ def stats():
     }
 
 
+# basically, hack config and populate it with fake data? fake data generated by DAL, but the rest is handled by this?
+
+from contextlib import contextmanager
+# todo take seed, or what?
+@contextmanager
+def fake_data(rows=1000):
+    # todo also disable cachew automatically for such things?
+    # TODO right, disabled_cachew won't work here because at that point, entries() is already wrapped?
+    # I guess need to fix this in cachew?
+    from .core.cachew import disabled_cachew
+    from .core.cfg import override_config
+    from tempfile import TemporaryDirectory
+    with disabled_cachew(), override_config(config) as cfg, TemporaryDirectory() as td:
+        tdir = Path(td)
+        cfg.export_path = tdir
+        f = tdir / 'rescuetime.json'
+        import json
+        f.write_text(json.dumps(dal.fake_data_generator(rows=rows)))
+        yield
+# TODO ok, now it's something that actually could run on CI!
+
+
+
 # todo not sure if I want to keep these here? vvv
 
-
-def print_groups():
-    for gr in groups():
-         print(f"{gr[0].dt}--{gr[-1].dt}")
-    # TODO merged db?
-    # TODO ok, it summarises my sleep intervals pretty well. I guess should adjust it for the fact I don't sleep during the day, and it would be ok!
-
-
 def fill_influxdb():
     from influxdb import InfluxDBClient # type: ignore
     client = InfluxDBClient()