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.venv/Lib/site-packages/altair/examples/tests/test_examples.py

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+import io
+import pkgutil
+
+import pytest
+
+from altair.utils.execeval import eval_block
+from altair import examples
+
+
+@pytest.fixture
+def require_altair_saver_png():
+    try:
+        import altair_saver  # noqa: F401
+    except ImportError:
+        pytest.skip("altair_saver not importable; cannot run saver tests")
+    if "png" not in altair_saver.available_formats('vega-lite'):
+        pytest.skip("altair_saver not configured to save to png")
+
+
+def iter_example_filenames():
+    for importer, modname, ispkg in pkgutil.iter_modules(examples.__path__):
+        if ispkg or modname.startswith('_'):
+            continue
+        yield modname + '.py'
+
+
+@pytest.mark.parametrize('filename', iter_example_filenames())
+def test_examples(filename: str):
+    source = pkgutil.get_data(examples.__name__, filename)
+    chart = eval_block(source)
+
+    if chart is None:
+        raise ValueError("Example file should define chart in its final "
+                         "statement.")
+    chart.to_dict()
+
+
+@pytest.mark.parametrize('filename', iter_example_filenames())
+def test_render_examples_to_png(require_altair_saver_png, filename):
+    source = pkgutil.get_data(examples.__name__, filename)
+    chart = eval_block(source)
+    out = io.BytesIO()
+    chart.save(out, format="png")
+    assert out.getvalue().startswith(b'\x89PNG')