tests/f2: improve error message for failed in assertions

By default, when one uses `in` assertions, upon failure newlines in any
of the two strings is escaped, and everything is printed in a single
line.

This commit allows one to pass `-vv` to print out the left and righthand
side unescaped, with each line of the output being its own line,
improving readability a lot when dealing with multiline outputs.

Change-Id: Iaf67a20fce57d375e2c62a8e8a0957b14eec26ef

tests/functional2/conftest.py

@@ -1,3 +1,5 @@
+import pytest
+
 pytest_plugins = (
     "testlib.fixtures.env",
     "testlib.fixtures.formatter",
@@ -10,6 +12,28 @@ pytest_plugins = (
     "testlib.fixtures.pytest_command",
 )
 
+
+def pytest_assertrepr_compare(config: pytest.Config, op: str, left: object, right: object) -> list[str] | None:
+    if not isinstance(left, str) or not isinstance(right, str) or op != "in":
+        return None
+    left: str
+    right: str
+
+    expl = [
+        f"{left} in {right}.",
+    ]
+
+    if config.get_verbosity():
+        expl.append("left:")
+        expl.extend([
+                        f"   {line}" for line in left.splitlines()
+                    ])
+        expl.append("right:")
+        expl.extend([
+                            f"    {line}" for line in right.splitlines()
+                        ])
+    return expl
+
 # the rest of this file is also a fork of pytest-tap v3.5 adjusted for lix use casess.
 # ideally this would be its own module, but xdist causes failures if it is. dunno why.