diff --git a/my/core/common.py b/my/core/common.py
index 2258af6..582708a 100644
--- a/my/core/common.py
+++ b/my/core/common.py
@@ -447,18 +447,64 @@ def _stat_iterable(it: Iterable[C]) -> Any:
     return res
 
 
+def test_stat_iterable() -> None:
+    from datetime import datetime, timedelta
+    from typing import NamedTuple
+
+    dd = datetime.utcfromtimestamp(123)
+    day = timedelta(days=3)
+
+    X = NamedTuple('X', [('x', int), ('d', datetime)])
+
+    def it():
+        yield RuntimeError('oops!')
+        for i in range(2):
+            yield X(x=i, d=dd + day * i)
+        yield RuntimeError('bad!')
+        for i in range(3):
+            yield X(x=i * 10, d=dd + day * (i * 10))
+        yield X(x=123, d=dd + day * 50)
+
+    res = _stat_iterable(it())
+    assert res['count']  == 1 + 2 + 1 + 3 + 1
+    assert res['errors'] == 1 + 1
+    assert res['last'] == dd + day * 50
+
+
 # experimental, not sure about it..
 def guess_datetime(x: Any) -> Optional[datetime]:
-    # todo support datacalsses
-    asdict = getattr(x, '_asdict', None)
-    if asdict is None:
+    # todo hmm implement withoutexception..
+    try:
+        d = asdict(x)
+    except:
         return None
-    # todo check if there are multiple?
-    for k, v in asdict().items():
+    for k, v in d.items():
         if isinstance(v, datetime):
             return v
     return None
 
+def test_guess_datetime() -> None:
+    from datetime import datetime
+    from dataclasses import dataclass
+    from typing import NamedTuple
+
+    dd = isoparse('2021-02-01T12:34:56Z')
+
+    # ugh.. https://github.com/python/mypy/issues/7281
+    A = NamedTuple('A', [('x', int)])
+    B = NamedTuple('B', [('x', int), ('created', datetime)])
+
+    assert guess_datetime(A(x=4)) is None
+    assert guess_datetime(B(x=4, created=dd)) == dd
+
+    @dataclass
+    class C:
+        a: datetime
+        x: int
+    assert guess_datetime(C(a=dd, x=435)) == dd
+    # TODO not sure what to return when multiple datetime fields?
+    # TODO test @property?
+
 
 def asdict(thing) -> Json:
     # todo primitive?
diff --git a/tests/cli.py b/tests/cli.py
new file mode 100644
index 0000000..1e3c560
--- /dev/null
+++ b/tests/cli.py
@@ -0,0 +1,4 @@
+from subprocess import check_call
+
+def test_lists_modules() -> None:
+    check_call(['hpi', 'modules'])
diff --git a/tests/core.py b/tests/core.py
index 0ffd225..4aa8173 100644
--- a/tests/core.py
+++ b/tests/core.py
@@ -13,3 +13,4 @@ we can run against the tests in my.core directly.
 from my.core.core_config import *
 from my.core.error       import *
 from my.core.util        import *
+from my.core.common      import *
diff --git a/tox.ini b/tox.ini
index d71c142..1a72477 100644
--- a/tox.ini
+++ b/tox.ini
@@ -24,6 +24,7 @@ commands =
     pip install orgparse
 
     python3 -m pytest                              \
+        tests/cli.py                               \
         tests/core.py                              \
         tests/misc.py                              \
         tests/get_files.py                         \
@@ -33,8 +34,8 @@ commands =
         tests/location.py                          \
         tests/tz.py                                \
         tests/calendar.py                          \
-        tests/config.py
-    hpi modules
+        tests/config.py                            \
+        {posargs}
 
 
 [testenv:demo]