changes for fixing the failing test

Author: vivekvedant

lib/matplotlib/axes/_axes.py

@@ -5748,9 +5748,10 @@ def _pcolorargs(self, funcname, *args, shading='auto', **kwargs):
 
         if shading == 'flat':
             if (Nx, Ny) != (ncols + 1, nrows + 1):
-                raise TypeError(f"Dimensions of X({Nx}) and y({Ny}) should"
-                                f" be one larger than C {C.shape} while using"
-                                f" shading='flat' see help({funcname})")
+                raise TypeError(f"Dimensions of C {C.shape} should"
+                                f" be one smaller than X({Nx}) and Y({Ny})"
+                                f" while using shading='flat'"
+                                f" see help({funcname})")
         else:    # ['nearest', 'gouraud']:
             if (Nx, Ny) != (ncols, nrows):
                 raise TypeError('Dimensions of C %s are incompatible with'

lib/matplotlib/tests/test_axes.py

@@ -1443,7 +1443,7 @@ def test_samesizepcolorflaterror():
     fig, ax = plt.subplots()
     x, y = np.meshgrid(np.arange(5), np.arange(3))
     Z = x + y
-    with pytest.raises(TypeError, match=r".*one larger than C"):
+    with pytest.raises(TypeError, match=r".*one smaller than X"):
         ax.pcolormesh(x, y, Z, shading='flat')