Fixed database typo and removed unnecessary class identifier.

venv/Lib/site-packages/matplotlib/tests/test_png.py

@@ -0,0 +1,52 @@
+from io import BytesIO
+from pathlib import Path
+
+import pytest
+
+from matplotlib.testing.decorators import image_comparison
+from matplotlib import pyplot as plt
+import matplotlib.cm as cm
+
+
+@image_comparison(['pngsuite.png'], tol=0.03)
+def test_pngsuite():
+    files = sorted(
+        (Path(__file__).parent / "baseline_images/pngsuite").glob("basn*.png"))
+
+    plt.figure(figsize=(len(files), 2))
+
+    for i, fname in enumerate(files):
+        data = plt.imread(fname)
+        cmap = None  # use default colormap
+        if data.ndim == 2:
+            # keep grayscale images gray
+            cmap = cm.gray
+        plt.imshow(data, extent=[i, i + 1, 0, 1], cmap=cmap)
+
+    plt.gca().patch.set_facecolor("#ddffff")
+    plt.gca().set_xlim(0, len(files))
+
+
+def test_truncated_file(tmpdir):
+    d = tmpdir.mkdir('test')
+    fname = str(d.join('test.png'))
+    fname_t = str(d.join('test_truncated.png'))
+    plt.savefig(fname)
+    with open(fname, 'rb') as fin:
+        buf = fin.read()
+    with open(fname_t, 'wb') as fout:
+        fout.write(buf[:20])
+
+    with pytest.raises(Exception):
+        plt.imread(fname_t)
+
+
+def test_truncated_buffer():
+    b = BytesIO()
+    plt.savefig(b)
+    b.seek(0)
+    b2 = BytesIO(b.read(20))
+    b2.seek(0)
+
+    with pytest.raises(Exception):
+        plt.imread(b2)