review action - hash library kernel

Author: bjlittle

pytest_mpl/plugin.py

@@ -351,8 +351,12 @@ def __init__(self,
                 emsg = f'Unrecognised hashing kernel {kernel!r} not supported.'
                 raise ValueError(emsg)
             kernel = requested
+            # Flag that the kernel has been user configured.
+            self.kernel_default = False
         else:
             kernel = DEFAULT_KERNEL
+            # Flag that the kernel has been configured by default.
+            self.kernel_default = True
         # Create the kernel.
         self.kernel = kernel_factory[kernel](self)
 
@@ -631,12 +635,15 @@ def compare_image_to_hash_library(self, item, fig, result_dir, summary=None):
                         f'in the hash library {str(hash_library_filename)!r}.')
                 pytest.fail(emsg)
             if kernel_name != self.kernel.name:
-                # TODO: we could be lenient here by raising a warning and hot-swap to
-                #       use the hash library kernel, instead of forcing a test failure?
-                emsg = (f'Hash library {str(hash_library_filename)!r} kernel '
-                        f'{kernel_name!r} does not match configured runtime '
-                        f'kernel {self.kernel.name!r}.')
-                pytest.fail(emsg)
+                if self.kernel_default:
+                    # Override the default kernel with the kernel configured
+                    # within the hash library.
+                    self.kernel = kernel_factory[kernel_name](self)
+                else:
+                    emsg = (f'Hash library {str(hash_library_filename)!r} kernel '
+                            f'{kernel_name!r} does not match configured runtime '
+                            f'kernel {self.kernel.name!r}.')
+                    pytest.fail(emsg)
 
         hash_name = self.generate_test_name(item)
         baseline_hash = hash_library.get(hash_name, None)

tests/test_pytest_mpl.py

@@ -492,14 +492,33 @@ def test_results_always(tmpdir):
                 assert json_res[json_image_key] is None
 
 
-def test_phash(tmpdir):
+@pytest.mark.parametrize("cla", ["--mpl-kernel=phash", ""])
+def test_phash(tmpdir, cla):
+    test_file = tmpdir.join("test.py").strpath
+    with open(test_file, "w") as fo:
+        fo.write(TEST_GENERATE)
+
+    # Filter out empty command-line-argument (cla) from command string.
+    command = list(filter(None,
+                          ["--mpl",
+                           cla,
+                           f"--mpl-hash-library={phash_library}",
+                           test_file]
+                          )
+                   )
+    code = call_pytest(command)
+    assert code == 0
+
+
+def test_phash__fail(tmpdir):
     test_file = tmpdir.join("test.py").strpath
     with open(test_file, "w") as fo:
         fo.write(TEST_GENERATE)
 
     command = ["--mpl",
-               "--mpl-kernel=phash",
+               "--mpl-kernel=sha256",
                f"--mpl-hash-library={phash_library}",
                test_file]
-    code = call_pytest(command)
-    assert code == 0
+
+    emsg = "'phash' does not match configured runtime kernel 'sha256'"
+    assert_pytest_fails_with(command, emsg)