Fix check for output format (#151)

* Fix output-format condition.

* Add successful test.

* Reformat.

changelogs/fragments/151-generate-output-format.yml

@@ -0,0 +1,2 @@
+bugfixes:
+  - "When multiple output formats are defined and ``antsibull-changelog generate`` is used with both ``--output`` and ``--output-format``, an error was displayed that ``--output-format`` must be specified (https://github.com/ansible-community/antsibull-changelog/issues/149, https://github.com/ansible-community/antsibull-changelog/pull/151)."

src/antsibull_changelog/cli.py

@@ -750,7 +750,7 @@ def command_generate(args: Any) -> int:  # pylint: disable=too-many-locals
             version=changes.latest_version,
             force_reload=args.reload_plugins,
         )
-    if output and len(config.output_formats) > 1:
+    if output and len(config.output_formats) > 1 and not output_format:
         print(
             "When an explicit output path is specified and more than one output format"
             " is configured, you need to explicitly specify an output format"

tests/functional/test_changelog_basic_collection.py

@@ -143,6 +143,37 @@ def test_changelog_release_empty(  # pylint: disable=redefined-outer-name
     )
     assert collection_changelog.diff().unchanged
 
+    assert (
+        collection_changelog.run_tool(
+            "generate",
+            ["-v", "--refresh", "--output", "extract.md", "--output-format", "md"],
+        )
+        == 0
+    )
+
+    diff = collection_changelog.diff()
+    assert diff.added_dirs == []
+    assert diff.added_files == ["extract.md"]
+    assert diff.removed_dirs == []
+    assert diff.removed_files == []
+    assert diff.changed_files == []
+    assert diff.file_contents["extract.md"].decode("utf-8") == (
+        r"""# Ansible Release Notes
+
+**Topics**
+- <a href="#v1-0-0">v1\.0\.0</a>
+  - <a href="#release-summary">Release Summary</a>
+
+<a id="v1-0-0"></a>
+## v1\.0\.0
+
+<a id="release-summary"></a>
+### Release Summary
+
+This is the first proper release\.
+"""
+    )
+
     assert (
         collection_changelog.run_tool(
             "release", ["-v", "--codename", "primetime", "--date", "2020-01-03"]