Improve test failure messages on warnings.

anntzer · anntzer · commit 335152fae005 · 2020-02-16T14:45:15.000+01:00
When a test fails due to a warning, this improves the failure message
from `assert 1 == 0 where 1 = len(WarningsChecker(record=True))` to the
actual warning message.
diff --git a/lib/matplotlib/tests/test_artist.py b/lib/matplotlib/tests/test_artist.py
@@ -219,10 +219,9 @@ def test_default_edges():
     ax4.add_patch(pp1)
 
 
-def test_properties(recwarn):
+def test_properties():
     ln = mlines.Line2D([], [])
-    ln.properties()
-    assert len(recwarn) == 0
+    ln.properties()  # Check that no warning is emitted.
 
 
 def test_setp():
diff --git a/lib/matplotlib/tests/test_axes.py b/lib/matplotlib/tests/test_axes.py
@@ -4723,13 +4723,12 @@ def test_length_one_hist():
     ax.hist([1])
 
 
-def test_pathological_hexbin(recwarn):
+def test_pathological_hexbin():
     # issue #2863
     mylist = [10] * 100
     fig, ax = plt.subplots(1, 1)
     ax.hexbin(mylist, mylist)
-    fig.savefig(io.BytesIO())
-    assert len(recwarn) == 0
+    fig.savefig(io.BytesIO())  # Check that no warning is emitted.
 
 
 def test_color_None():
diff --git a/lib/matplotlib/tests/test_cbook.py b/lib/matplotlib/tests/test_cbook.py
@@ -335,10 +335,10 @@ def test_normalize_kwargs_fail(inp, kwargs_to_norm):
 
 @pytest.mark.parametrize('inp, expected, kwargs_to_norm',
                          pass_mapping)
-def test_normalize_kwargs_pass(inp, expected, kwargs_to_norm, recwarn):
+def test_normalize_kwargs_pass(inp, expected, kwargs_to_norm):
     with cbook._suppress_matplotlib_deprecation_warning():
+        # No other warning should be emitted.
         assert expected == cbook.normalize_kwargs(inp, **kwargs_to_norm)
-    assert len(recwarn) == 0
 
 
 def test_warn_external_frame_embedded_python():
@@ -574,13 +574,12 @@ def test_safe_first_element_pandas_series(pd):
     assert actual == 0
 
 
-def test_make_keyword_only(recwarn):
+def test_make_keyword_only():
     @cbook._make_keyword_only("3.0", "arg")
     def func(pre, arg, post=None):
         pass
 
-    func(1, arg=2)
-    assert len(recwarn) == 0
+    func(1, arg=2)  # Check that no warning is emitted.
 
     with pytest.warns(MatplotlibDeprecationWarning):
         func(1, 2)
diff --git a/lib/matplotlib/tests/test_colors.py b/lib/matplotlib/tests/test_colors.py
@@ -890,7 +890,7 @@ def test_tableau_order():
     assert list(mcolors.TABLEAU_COLORS.values()) == dflt_cycle
 
 
-def test_ndarray_subclass_norm(recwarn):
+def test_ndarray_subclass_norm():
     # Emulate an ndarray subclass that handles units
     # which objects when adding or subtracting with other
     # arrays. See #6622 and #8696
@@ -912,9 +912,7 @@ def __add__(self, other):
         assert_array_equal(norm(mydata), norm(data))
         fig, ax = plt.subplots()
         ax.imshow(mydata, norm=norm)
-        fig.canvas.draw()
-        assert len(recwarn) == 0
-        recwarn.clear()
+        fig.canvas.draw()  # Check that no warning is emitted.
 
 
 def test_same_color():
diff --git a/lib/matplotlib/tests/test_contour.py b/lib/matplotlib/tests/test_contour.py
@@ -279,14 +279,11 @@ def test_internal_cpp_api_2():
 
 def test_circular_contour_warning():
     # Check that almost circular contours don't throw a warning
-    with pytest.warns(None) as record:
-        x, y = np.meshgrid(np.linspace(-2, 2, 4), np.linspace(-2, 2, 4))
-        r = np.hypot(x, y)
-
-        plt.figure()
-        cs = plt.contour(x, y, r)
-        plt.clabel(cs)
-    assert len(record) == 0
+    x, y = np.meshgrid(np.linspace(-2, 2, 4), np.linspace(-2, 2, 4))
+    r = np.hypot(x, y)
+    plt.figure()
+    cs = plt.contour(x, y, r)
+    plt.clabel(cs)
 
 
 @pytest.mark.parametrize("use_clabeltext, contour_zorder, clabel_zorder",
diff --git a/lib/matplotlib/tests/test_image.py b/lib/matplotlib/tests/test_image.py
@@ -975,9 +975,8 @@ def test_imshow_masked_interpolation():
         ax.axis('off')
 
 
-def test_imshow_no_warn_invalid(recwarn):
-    plt.imshow([[1, 2], [3, np.nan]])
-    assert len(recwarn) == 0
+def test_imshow_no_warn_invalid():
+    plt.imshow([[1, 2], [3, np.nan]])  # Check that no warning is emitted.
 
 
 @pytest.mark.parametrize(
diff --git a/lib/matplotlib/tests/test_legend.py b/lib/matplotlib/tests/test_legend.py
@@ -570,6 +570,4 @@ def test_no_warn_big_data_when_loc_specified():
     for idx in range(1000):
         ax.plot(np.arange(5000), label=idx)
     legend = ax.legend('best')
-    with pytest.warns(None) as records:
-        fig.draw_artist(legend)
-    assert len(records) == 0
+    fig.draw_artist(legend)  # Check that no warning is emitted.
diff --git a/lib/matplotlib/tests/test_quiver.py b/lib/matplotlib/tests/test_quiver.py
@@ -71,25 +71,23 @@ def test_quiver_arg_sizes():
         plt.quiver(X2, X2, X2, X2, X3)
 
 
-def test_no_warnings(recwarn):
+def test_no_warnings():
     fig, ax = plt.subplots()
     X, Y = np.meshgrid(np.arange(15), np.arange(10))
     U = V = np.ones_like(X)
     phi = (np.random.rand(15, 10) - .5) * 150
     ax.quiver(X, Y, U, V, angles=phi)
-    fig.canvas.draw()
-    assert len(recwarn) == 0
+    fig.canvas.draw()  # Check that no warning is emitted.
 
 
-def test_zero_headlength(recwarn):
+def test_zero_headlength():
     # Based on report by Doug McNeil:
     # http://matplotlib.1069221.n5.nabble.com/quiver-warnings-td28107.html
     fig, ax = plt.subplots()
     X, Y = np.meshgrid(np.arange(10), np.arange(10))
     U, V = np.cos(X), np.sin(Y)
     ax.quiver(U, V, headlength=0, headaxislength=0)
-    fig.canvas.draw()
-    assert len(recwarn) == 0
+    fig.canvas.draw()  # Check that no warning is emitted.
 
 
 @image_comparison(['quiver_animated_test_image.png'])
diff --git a/lib/matplotlib/tests/test_rcparams.py b/lib/matplotlib/tests/test_rcparams.py
@@ -506,11 +506,9 @@ def test_if_rctemplate_would_be_valid(tmpdir):
     fname = str(d.join('testrcvalid.temp'))
     with open(fname, "w") as f:
         f.writelines(newlines)
-    with pytest.warns(None) as record:
-        mpl.rc_params_from_file(fname,
-                                fail_on_error=True,
-                                use_default_template=False)
-        assert len(record) == 0
+    mpl.rc_params_from_file(fname,
+                            fail_on_error=True,  # Test also fails on warning.
+                            use_default_template=False)
 
 
 @pytest.mark.skipif(sys.platform != "linux", reason="Linux only")
