test(m1): add conftest fixtures and golden helpers

tests/test_helpers_selfcheck.py

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+"""The test harness tests itself (plan Step 6).
+
+Everything downstream of here trusts these helpers, so a golden comparator
+that silently passes, or a pristine-fixture guard that never trips, would not
+announce itself -- it would just make the rest of the suite quietly weaker.
+The four tests below are the ones that would catch that: each asserts the
+helper can FAIL, not merely that it can pass.
+
+`assert_golden` takes its update flag as an argument rather than reading the
+pytest config itself, so the rewrite path is reachable from a test without
+re-running pytest inside pytest. The flag wiring is asserted separately, on
+the registered option.
+
+Style note: this file follows tests/test_jsonl.py.
+"""
+
+import os
+
+import pytest
+
+from helpers import golden, workspace
+
+
+def test_assert_golden_passes_unchanged_and_fails_on_a_change(tmp_path):
+    reference = str(tmp_path / "dagens.txt")
+    with open(reference, "w", encoding="utf-8") as handle:
+        handle.write("Tromsø: 2 saker\n")
+
+    golden.assert_golden(reference, "Tromsø: 2 saker\n")
+
+    with pytest.raises(AssertionError) as caught:
+        golden.assert_golden(reference, "Tromsø: 3 saker\n")
+    # The message has to carry the diff; "golden mismatch" alone sends the
+    # reader back to the file to work out what moved.
+    assert "3 saker" in str(caught.value)
+
+
+def test_update_golden_rewrites_the_file_and_the_flag_is_registered(tmp_path, request):
+    reference = str(tmp_path / "dagens.txt")
+    with open(reference, "w", encoding="utf-8") as handle:
+        handle.write("gammelt\n")
+
+    golden.assert_golden(reference, "nytt\n", update=True)
+    assert open(reference, encoding="utf-8").read() == "nytt\n"
+
+    # Regeneration is deliberate: off unless the operator asks for it.
+    assert request.config.getoption("--update-golden") is False
+
+
+def test_make_case_produces_a_case_that_read_jsonl_can_read(empty_workspace, frozen_today):
+    sak_id = workspace.make_case(
+        empty_workspace,
+        arbeidsgiver="Fjordtek AS",
+        rolle="Rådgiver",
+        year_month="2026-09",
+        events=[workspace.event("opprettet", days_ago=3), workspace.event("soknad_sendt", days_ago=1)],
+    )
+    assert sak_id == "2026-09-fjordtek-as-radgiver"
+
+    log = os.path.join(empty_workspace, "saker", sak_id, "logg.jsonl")
+    records = workspace.read_jsonl(log)
+    assert [rec["hendelse"] for rec in records] == ["opprettet", "soknad_sendt"]
+
+    meta, _ = workspace.frontmatter(os.path.join(empty_workspace, "saker", sak_id, "sak.md"))
+    assert meta["sak_id"] == sak_id
+    assert meta["arbeidsgiver"] == "Fjordtek AS"
+    assert frozen_today == "2026-09-15"
+
+
+def test_the_pristine_guard_trips_when_the_corpus_is_written_to(tmp_path):
+    corpus = tmp_path / "fixtures"
+    corpus.mkdir()
+    (corpus / "kandidat.md").write_text("opprinnelig\n", encoding="utf-8")
+
+    before = workspace.snapshot_tree(str(corpus))
+    workspace.assert_tree_unchanged(str(corpus), before)  # nothing moved yet
+
+    (corpus / "kandidat.md").write_text("endret av en test\n", encoding="utf-8")
+    with pytest.raises(AssertionError) as caught:
+        workspace.assert_tree_unchanged(str(corpus), before)
+    assert "kandidat.md" in str(caught.value)
+
+    # A new file is a mutation too -- a test that drops output into the corpus
+    # poisons every later run just as surely as one that edits a fixture.
+    restored = workspace.snapshot_tree(str(corpus))
+    (corpus / "uventet.txt").write_text("x\n", encoding="utf-8")
+    with pytest.raises(AssertionError):
+        workspace.assert_tree_unchanged(str(corpus), restored)