Little refactoring and added tests for case when explanation should not be generated.

Author: Victor Maryama

src/_pytest/assertion/rewrite.py

@@ -543,7 +543,7 @@ def _call_assertion_pass(lineno, orig, expl):
 def _check_if_assertionpass_impl():
     """Checks if any plugins implement the pytest_assertion_pass hook
     in order not to generate explanation unecessarily (might be expensive)"""
-    return True if util._assertion_pass is not None else False
+    return True if util._assertion_pass else False
 
 
 unary_map = {ast.Not: "not %s", ast.Invert: "~%s", ast.USub: "-%s", ast.UAdd: "+%s"}
@@ -883,7 +883,6 @@ def visit_Assert(self, assert_):
             [],
         )
         main_test = ast.If(negation, [raise_], [hook_impl_test])
-        # main_test = ast.If(negation, [raise_], [hook_call_pass])
 
         self.statements.extend(self.expl_stmts)
         self.statements.append(main_test)

testing/test_assertrewrite.py

@@ -1474,3 +1474,28 @@ def test_simple():
         result.stdout.fnmatch_lines(
             "*Assertion Passed: a + b == c + d (1 + 2) == (3 + 0) at line 7*"
         )
+
+    def test_hook_not_called_without_hookimpl(self, testdir, monkeypatch):
+        """Assertion pass should not be called (and hence formatting should
+        not occur) if there is no hook declared for pytest_assertion_pass"""
+
+        def raise_on_assertionpass(*_, **__):
+            raise Exception("Assertion passed called when it shouldn't!")
+
+        monkeypatch.setattr(_pytest.assertion.rewrite,
+                            "_call_assertion_pass",
+                            raise_on_assertionpass)
+
+        testdir.makepyfile(
+            """
+            def test_simple():
+                a=1
+                b=2
+                c=3
+                d=0
+
+                assert a+b == c+d
+            """
+        )
+        result = testdir.runpytest()
+        result.assert_outcomes(passed=1)