docmument new format='svg_inline' and add test coverage

- also: reorder `FORMATS`
- follow-up to bff786f
- see #233 and #237

Author: xflr6

CHANGES.rst

@@ -5,6 +5,10 @@ Changelog
 Version 0.21 (in development)
 -----------------------------
 
+Add support for ```format='svg_inline'``, available since upstream Graphviz 10.0.1.
+Produces header-less SVG suitable for inlining into HTML
+(see https://www.graphviz.org/docs/outputs/svg/).
+
 Switch project to ``pyproject.toml`` and build to `python -m build`) (https://build.pypa.io).
 This changes the source distribution formar from `.zip` to PEP 625 compliant
 `.tar.gz`` (https://peps.python.org/pep-0625/).

docs/piped_output.rst

@@ -33,7 +33,8 @@ of your :class:`.Graph` or :class:`.Digraph` object:
     Because :meth:`~.Graph.pipe` returns the raw ``stdout``
     from the layout subprocess by default (:class:`bytes`),
     you usually want to decode the return value
-    when piping into formats like ``'svg'`` or ``'plain'``,
+    when piping into formats like ``'svg'``, ``'svg_inline'`` or ``'plain'``,
+    e.g. by passing ``encoding='utf-8'``.
 
 .. caution::
 

graphviz/parameters/formats.py

@@ -33,7 +33,7 @@
            'ps2',
            'psd',
            'sgi',
-           'svg', 'svgz', 'svg_inline',
+           'svg', 'svg_inline', 'svgz',  # svg_linline: Graphviz 10.0.1
            'tga',
            'tif', 'tiff',
            'tk',

tests/test_all_classes.py

@@ -224,9 +224,16 @@ def test_save_mocked(mocker, dot, filename='nonfilename', directory='nondirector
 
 
 @pytest.mark.exe
-def test_pipe(dot, encoding='utf-8'):
-    svg = dot.pipe(format='svg', encoding=encoding)
-    assert svg.startswith('<?xml ')
+@pytest.mark.parametrize(
+    'plain_text_format, expected_start',
+    [('svg', '<?xml version='),
+     # https://gitlab.com/graphviz/graphviz/-/blob/main/CHANGELOG.md#1001--2024-02-11
+     pytest.param('svg_inline', '<!-- Generated by graphviz version ',
+                  marks=pytest.mark.xfail('graphviz.version() < (10, 0, 1)',
+                                          reason='needs Graphviz 10 or later'))])
+def test_pipe(dot, plain_text_format, expected_start):
+    result = dot.pipe(format=plain_text_format, encoding='utf-8')
+    assert result.startswith(expected_start)
 
 
 @pytest.mark.parametrize(