assertoutcomes() only accepts plural forms

Fix pytest-dev#6505

changelog/6505.breaking.rst

@@ -0,0 +1,20 @@
+``Testdir.run().parseoutcomes()`` now always returns the parsed nouns in plural form.
+
+Originally ``parseoutcomes()`` would always returns the nouns in plural form, but a change
+meant to improve the terminal summary by using singular form single items (``1 warning`` or ``1 error``)
+caused an unintended regression by changing the keys returned by ``parseoutcomes()``.
+
+Now the API guarantees to always return the plural form, so calls like this:
+
+.. code-block:: python
+
+    result = testdir.runpytest()
+    result.assert_outcomes(error=1)
+
+Need to be changed to:
+
+
+.. code-block:: python
+
+    result = testdir.runpytest()
+    result.assert_outcomes(errors=1)

src/_pytest/pytester.py

@@ -452,28 +452,47 @@ def __repr__(self) -> str:
         )
 
     def parseoutcomes(self) -> Dict[str, int]:
-        """Return a dictionary of outcomestring->num from parsing the terminal
+        """Return a dictionary of outcome noun -> count from parsing the terminal
         output that the test process produced.
 
+        The returned nouns will always be in plural form::
+
+            ======= 1 failed, 1 passed, 1 warning, 1 error in 0.13s ====
+
+        Will return ``{"failed": 1, "passed": 1, "warnings": 1, "errors": 1}``
+        """
+        return self.parse_summary_nouns(self.outlines)
+
+    @classmethod
+    def parse_summary_nouns(cls, lines) -> Dict[str, int]:
+        """Extracts the nouns from a pytest terminal summary line.
+
+        It always returns the plural noun for consistency::
+
+            ======= 1 failed, 1 passed, 1 warning, 1 error in 0.13s ====
+
+        Will return ``{"failed": 1, "passed": 1, "warnings": 1, "errors": 1}``
         """
-        for line in reversed(self.outlines):
+        for line in reversed(lines):
             if rex_session_duration.search(line):
                 outcomes = rex_outcome.findall(line)
                 ret = {noun: int(count) for (count, noun) in outcomes}
                 break
         else:
             raise ValueError("Pytest terminal summary report not found")
-        if "errors" in ret:
-            assert "error" not in ret
-            ret["error"] = ret.pop("errors")
-        return ret
+
+        to_plural = {
+            "warning": "warnings",
+            "error": "errors",
+        }
+        return {to_plural.get(k, k): v for k, v in ret.items()}
 
     def assert_outcomes(
         self,
         passed: int = 0,
         skipped: int = 0,
         failed: int = 0,
-        error: int = 0,
+        errors: int = 0,
         xpassed: int = 0,
         xfailed: int = 0,
     ) -> None:
@@ -487,15 +506,15 @@ def assert_outcomes(
             "passed": d.get("passed", 0),
             "skipped": d.get("skipped", 0),
             "failed": d.get("failed", 0),
-            "error": d.get("error", 0),
+            "errors": d.get("errors", 0),
             "xpassed": d.get("xpassed", 0),
             "xfailed": d.get("xfailed", 0),
         }
         expected = {
             "passed": passed,
             "skipped": skipped,
             "failed": failed,
-            "error": error,
+            "errors": errors,
             "xpassed": xpassed,
             "xfailed": xfailed,
         }

testing/python/fixtures.py

@@ -4342,6 +4342,6 @@ def test_fixt(custom):
     )
     expected = "E               ValueError: custom did not yield a value"
     result = testdir.runpytest()
-    result.assert_outcomes(error=1)
+    result.assert_outcomes(errors=1)
     result.stdout.fnmatch_lines([expected])
     assert result.ret == ExitCode.TESTS_FAILED

testing/test_pytester.py

@@ -763,9 +763,38 @@ def test_error2(bad_fixture):
     """
     )
     result = testdir.runpytest(str(p1))
-    result.assert_outcomes(error=2)
+    result.assert_outcomes(errors=2)
 
-    assert result.parseoutcomes() == {"error": 2}
+    assert result.parseoutcomes() == {"errors": 2}
+
+
+def test_parse_summary_line_always_plural():
+    """Parsing summaries always returns plural nouns (#6505)"""
+    lines = [
+        "some output 1",
+        "some output 2",
+        "======= 1 failed, 1 passed, 1 warning, 1 error in 0.13s ====",
+        "done.",
+    ]
+    assert pytester.RunResult.parse_summary_nouns(lines) == {
+        "errors": 1,
+        "failed": 1,
+        "passed": 1,
+        "warnings": 1,
+    }
+
+    lines = [
+        "some output 1",
+        "some output 2",
+        "======= 1 failed, 1 passed, 2 warnings, 2 errors in 0.13s ====",
+        "done.",
+    ]
+    assert pytester.RunResult.parse_summary_nouns(lines) == {
+        "errors": 2,
+        "failed": 1,
+        "passed": 1,
+        "warnings": 2,
+    }
 
 
 def test_makefile_joins_absolute_path(testdir: Testdir) -> None: