diff --git a/README.md b/README.md
index 0f9e49e..d9043ae 100644
--- a/README.md
+++ b/README.md
@@ -78,6 +78,12 @@ To test:
 pytest
 ```
 
+Generate a coverage report with:
+
+```
+pytest --cov-report term-missing --cov yaml2ics
+```
+
 [black](https://github.com/psf/black) and other linters are used to auto-format
 files (and enforced by CI). To install the git hooks, use `pre-commit install`.
 To run the tests/auto-formatting manually, use `pre-commit run --all-files`.
diff --git a/tests/test_cli.py b/tests/test_cli.py
new file mode 100644
index 0000000..529b0a4
--- /dev/null
+++ b/tests/test_cli.py
@@ -0,0 +1,47 @@
+import os
+import sys
+
+import pytest
+
+from yaml2ics import event_from_yaml, main
+
+basedir = os.path.abspath(os.path.join(os.path.dirname(__file__)))
+example_calendar = os.path.join(basedir, "../example/test_calendar.yaml")
+
+
+def test_cli(monkeypatch):
+    with monkeypatch.context() as m:
+        m.setattr(sys, "argv", ["yaml2ics.py", example_calendar])
+        main()
+
+    with monkeypatch.context() as m:
+        m.setattr(sys, "argv", ["yaml2ics.py"])
+
+        with pytest.raises(RuntimeError) as e:
+            main()
+            assert "Usage:" in str(e)
+
+    with monkeypatch.context() as m:
+        m.setattr(sys, "argv", ["yaml2ics.py", "syzygy.yaml"])
+
+        with pytest.raises(RuntimeError) as e:
+            main()
+            assert "is not a file" in str(e)
+
+
+def test_errors():
+    with pytest.raises(RuntimeError) as e:
+        event_from_yaml({"repeat": {"interval": {}}})
+    assert "interval must specify" in str(e)
+
+    with pytest.raises(RuntimeError) as e:
+        event_from_yaml({"ics": "123"})
+    assert "Invalid custom ICS" in str(e)
+
+    with pytest.raises(RuntimeError) as e:
+        event_from_yaml({"repeat": {"interval": {"weeks": 1}}})
+    assert "must specify end date for repeating events" in str(e)
+
+    with pytest.raises(RuntimeError) as e:
+        event_from_yaml({"repeat": {"interval": {"epochs": 4}}})
+    assert "expected interval to be specified in seconds, minutes" in str(e)
diff --git a/yaml2ics.py b/yaml2ics.py
index 77ad7f3..df0cdef 100644
--- a/yaml2ics.py
+++ b/yaml2ics.py
@@ -75,25 +75,20 @@ def event_from_yaml(event_yaml: dict, tz: datetime.tzinfo = None) -> ics.Event:
         interval = repeat["interval"]
 
         if not len(interval) == 1:
-            print(
+            raise RuntimeError(
                 "Error: interval must specify seconds, minutes, hours, days, "
-                "weeks, months, or years only",
-                file=sys.stderr,
+                "weeks, months, or years only"
             )
-            sys.exit(-1)
 
         interval_measure = list(interval.keys())[0]
         if interval_measure not in interval_type:
-            print(
+            raise RuntimeError(
                 "Error: expected interval to be specified in seconds, minutes, "
                 "hours, days, weeks, months, or years only",
-                file=sys.stderr,
             )
-            sys.exit(-1)
 
         if "until" not in repeat:
-            print("Error: must specify end date for repeating events", file=sys.stderr)
-            sys.exit(-1)
+            raise RuntimeError("Error: must specify end date for " "repeating events")
 
         # This causes zero-length events, I guess overriding whatever duration
         # might have been specified
@@ -131,6 +126,8 @@ def event_from_yaml(event_yaml: dict, tz: datetime.tzinfo = None) -> ics.Event:
 
     if ics_custom:
         for line in ics_custom.split("\n"):
+            if not line:
+                continue
             if ":" not in line:
                 raise RuntimeError(
                     f"Invalid custom ICS (expected `fieldname:value`):\n  {line}"
@@ -191,19 +188,21 @@ def files_to_calendar(files: list) -> ics.Calendar:
 
 def main():
     if len(sys.argv) < 2:
-        print("Usage: yaml2ics.py FILE1.yaml FILE2.yaml ...")
-        sys.exit(-1)
+        raise RuntimeError("Usage: yaml2ics.py FILE1.yaml FILE2.yaml ...")
 
     files = sys.argv[1:]
     for f in files:
         if not os.path.isfile(f):
-            print(f"Error: {f} is not a file", file=sys.stderr)
-            sys.exit(-1)
+            raise RuntimeError(f"Error: {f} is not a file")
 
     calendar = files_to_calendar(files)
 
     print(calendar.serialize())
 
 
-if __name__ == "__main__":
-    main()
+if __name__ == "__main__":  # pragma: no cover
+    try:
+        main()
+    except Exception as e:
+        print(e, file=sys.stderr)
+        sys.exit(-1)