terminal: fix crash in header reporting when testpaths is used without cli arguments

changelog/7814.bugfix.rst

@@ -0,0 +1 @@
+Fixed crash in header reporting when :confval:`testpaths` is used without CLI arguments (regression in 6.1.0).

src/_pytest/terminal.py

@@ -718,9 +718,11 @@ def pytest_report_header(self, config: Config) -> List[str]:
         if config.inipath:
             line += ", configfile: " + bestrelpath(config.rootpath, config.inipath)
 
-        testpaths = config.getini("testpaths")
+        testpaths = config.getini("testpaths")  # type: List[str]
         if testpaths and config.args == testpaths:
-            rel_paths = [bestrelpath(config.rootpath, x) for x in testpaths]
+            rel_paths = [
+                bestrelpath(config.rootpath, Path(absolutepath(x))) for x in testpaths
+            ]
             line += ", testpaths: {}".format(", ".join(rel_paths))
         result = [line]
 

testing/test_terminal.py

@@ -18,6 +18,7 @@
 from _pytest._io.wcwidth import wcswidth
 from _pytest.config import Config
 from _pytest.config import ExitCode
+from _pytest.monkeypatch import MonkeyPatch
 from _pytest.pathlib import Path
 from _pytest.pytester import Testdir
 from _pytest.reports import BaseReport
@@ -749,6 +750,24 @@ def test_header(self, testdir):
         result = testdir.runpytest("tests")
         result.stdout.fnmatch_lines(["rootdir: *test_header0, configfile: tox.ini"])
 
+    def test_header_testpaths_are_relative(
+        self, testdir: Testdir, monkeypatch: MonkeyPatch
+    ) -> None:
+        """Regresstion test for #7814."""
+        testdir.tmpdir.join("tests").ensure_dir()
+        testdir.makeini(
+            """
+            [pytest]
+            testpaths = {}/tests
+        """.format(
+                testdir.tmpdir
+            )
+        )
+        result = testdir.runpytest()
+        result.stdout.fnmatch_lines(
+            ["rootdir: *are_relative0, configfile: tox.ini, testpaths: tests"]
+        )
+
     def test_no_header(self, testdir):
         testdir.tmpdir.join("tests").ensure_dir()
         testdir.tmpdir.join("gui").ensure_dir()