Final acceptance: Консольная утилита поиска и скачивания изображений для вызова ИИ-агентом (#18)

Co-authored-by: AI Tester <ai-tester@git.p2prod.ru>

tests/test_images.py

@@ -0,0 +1,654 @@
+"""Tests for byte-based format and size filtering.
+
+Two layers are covered:
+
+* :mod:`tools.images` -- the stdlib-only detector and the stdlib-only builders
+  for the two accepted formats, so fixtures are real images rather than magic
+  strings;
+* the CLI search path -- candidates are filtered on the *downloaded bytes*, so
+  a source that mislabels a file, claims the wrong size or serves an unreadable
+  body produces the correct ``ok`` / ``no_format`` / ``no_size`` /
+  ``access_error`` answer.  Every CLI test injects a fake byte-fetch callable,
+  so nothing here touches the network.
+"""
+
+from __future__ import annotations
+
+import json
+import struct
+from typing import Any, Mapping, Sequence
+
+import pytest
+
+from tools import envelope, example, images
+from tools.errors import SourceAccessError
+from tools.images import ImageFormatError, ImageInfo
+
+# ---------------------------------------------------------------------------
+# Real-format builders used as fixtures
+# ---------------------------------------------------------------------------
+
+
+def png_payload(width: int, height: int) -> bytes:
+    """A real PNG built with :func:`tools.images.png_bytes`."""
+
+    return images.png_bytes(width, height)
+
+
+def ico_payload(width: int, height: int) -> bytes:
+    """A real ICO (PNG-compressed entry) built with :func:`tools.images.ico_bytes`."""
+
+    return images.ico_bytes(width, height)
+
+
+def gif_payload(width: int = 100, height: int = 100) -> bytes:
+    """A payload whose real format is GIF, i.e. one we must never accept."""
+
+    return b"GIF89a" + struct.pack("<HH", width, height) + b"\x00" * 8
+
+
+def jpeg_payload() -> bytes:
+    """A payload whose real format is JPEG, i.e. another format we must not accept."""
+
+    return b"\xff\xd8\xff\xe0" + b"\x00" * 12
+
+
+def svg_payload(width: int = 100, height: int = 100) -> bytes:
+    """A real SVG document, the most common non-bitmap hit on a live source."""
+
+    return (
+        '<?xml version="1.0" encoding="UTF-8"?>\n'
+        f'<svg xmlns="http://www.w3.org/2000/svg" width="{width}" height="{height}"></svg>\n'
+    ).encode("utf-8")
+
+
+def tiff_payload() -> bytes:
+    """A payload whose real format is TIFF."""
+
+    return b"II*\x00" + b"\x00" * 16
+
+
+def pdf_payload() -> bytes:
+    """A payload whose real format is PDF, served by document-friendly sources."""
+
+    return b"%PDF-1.7\n%\xe2\xe3\xcf\xd3\n"
+
+
+# ---------------------------------------------------------------------------
+# tools.images: detection
+# ---------------------------------------------------------------------------
+
+
+def test_png_bytes_builds_a_png_with_the_requested_dimensions() -> None:
+    payload = png_payload(13, 7)
+
+    assert payload.startswith(images.PNG_SIGNATURE)
+    assert images.detect_format(payload) == images.PNG
+    assert images.inspect_image(payload) == ImageInfo(format="png", width=13, height=7)
+    # The IHDR chunk really carries the dimensions, so the bytes are the source
+    # of truth rather than a helper function agreeing with itself.
+    assert payload[12:16] == b"IHDR"
+    assert struct.unpack(">II", payload[16:24]) == (13, 7)
+    assert images.read_png_dimensions(payload) == (13, 7)
+
+
+def test_ico_bytes_builds_a_directory_that_reports_the_requested_sizes() -> None:
+    payload = ico_payload(48, 37)
+
+    assert images.detect_format(payload) == images.ICO
+    assert images.inspect_image(payload) == ImageInfo(format="ico", width=48, height=37)
+    # One directory entry, and its data range lies inside the payload.
+    reserved, kind, count = struct.unpack("<HHH", payload[:6])
+    assert (reserved, kind, count) == (0, 1, 1)
+    _w, _h, _colours, _reserved, _planes, _bits, size, offset = struct.unpack("<BBBBHHII", payload[6:22])
+    assert offset + size == len(payload)
+
+
+def test_ico_maximum_dimension_uses_the_zero_encoding() -> None:
+    payload = ico_payload(256, 256)
+
+    assert payload[6] == 0 and payload[7] == 0
+    assert images.read_ico_dimensions(payload) == (256, 256)
+
+
+def test_ico_dimensions_use_the_largest_directory_entry() -> None:
+    payload = images.ico_bytes(16, 16, frames=[(16, 16), (32, 32), (256, 256)])
+
+    assert len(images.ico_entries(payload)) == 3
+    assert images.read_ico_dimensions(payload) == (256, 256)
+    assert images.inspect_image(payload).format == "ico"
+
+
+@pytest.mark.parametrize(
+    ("payload", "expected"),
+    [
+        (png_payload(2, 2), images.PNG),
+        (ico_payload(2, 2), images.ICO),
+        (gif_payload(), images.GIF),
+        (jpeg_payload(), images.JPEG),
+        (b"BM" + b"\x00" * 20, images.BMP),
+        (b"RIFF" + b"\x00\x00\x00\x00" + b"WEBP" + b"\x00" * 8, images.WEBP),
+        (svg_payload(), images.SVG),
+        (svg_payload().replace(b"<?xml", b"\xef\xbb\xbf<?xml", 1), images.SVG),
+        (tiff_payload(), images.TIFF),
+        (b"MM\x00*" + b"\x00" * 16, images.TIFF),
+        (pdf_payload(), images.PDF),
+    ],
+)
+def test_detect_format_names_the_real_format(payload: bytes, expected: str) -> None:
+    assert images.detect_format(payload) == expected
+
+
+@pytest.mark.parametrize("payload", [b"", b"payload", b"not-an-image", b"<html></html>"])
+def test_detect_format_returns_none_for_non_images(payload: bytes) -> None:
+    assert images.detect_format(payload) is None
+
+
+@pytest.mark.parametrize("payload", [gif_payload(), jpeg_payload(), svg_payload(), tiff_payload(), pdf_payload()])
+def test_inspect_image_rejects_formats_whose_size_is_not_readable(payload: bytes) -> None:
+    with pytest.raises(ImageFormatError) as excinfo:
+        images.inspect_image(payload)
+
+    assert excinfo.value.code == "image_unreadable"
+    # The format is named, so the CLI can report it as another format rather
+    # than as an access problem.
+    assert excinfo.value.details["format"] == images.detect_format(payload)
+
+
+@pytest.mark.parametrize(
+    "payload",
+    [
+        b"not-an-image",
+        images.PNG_SIGNATURE,
+        images.PNG_SIGNATURE + struct.pack(">I", 13) + b"IDAT" + b"\x00" * 13,
+        b"\x00\x00\x01\x00" + struct.pack("<HHH", 0, 1, 2),
+        b"\x00\x00\x01\x00" + struct.pack("<HHH", 0, 1, 1) + struct.pack("<BBBBHHII", 16, 16, 0, 0, 1, 32, 999, 22),
+    ],
+)
+def test_inspect_image_rejects_unreadable_payloads(payload: bytes) -> None:
+    with pytest.raises(ImageFormatError):
+        images.inspect_image(payload)
+
+
+def test_png_dimensions_reject_a_zero_sized_image() -> None:
+    payload = images.PNG_SIGNATURE + struct.pack(">I", 13) + b"IHDR" + struct.pack(">IIBBBBB", 0, 0, 8, 6, 0, 0, 0)
+
+    with pytest.raises(ImageFormatError):
+        images.read_png_dimensions(payload)
+
+
+# ---------------------------------------------------------------------------
+# CLI search path: filtering on downloaded bytes
+# ---------------------------------------------------------------------------
+
+
+class StubCandidate:
+    """Candidate whose bytes are supplied by a fake fetch callable."""
+
+    def __init__(
+        self,
+        title: str,
+        url: str,
+        *,
+        payload: bytes | None = None,
+        error: Exception | None = None,
+        mime_type: str | None = None,
+        width: int | None = None,
+        height: int | None = None,
+    ) -> None:
+        self.source_id = "fake"
+        self.title = title
+        self.file_url = url
+        self.page_url = url + ".html"
+        # Deliberately misleading metadata: filtering must ignore all of this.
+        self.mime_type = mime_type
+        self.width = width
+        self.height = height
+        self._payload = payload
+        self._error = error
+        self.fetch_calls = 0
+
+    def fetch_bytes(self) -> bytes:
+        self.fetch_calls += 1
+        if self._error is not None:
+            raise self._error
+        assert self._payload is not None
+        return self._payload
+
+
+class StubRegistry:
+    """Registry stand-in that returns a fixed candidate list."""
+
+    def __init__(self, candidates: Sequence[StubCandidate]) -> None:
+        self.candidates = list(candidates)
+        self.calls: list[tuple[str, str, int]] = []
+
+    def available_sources(self) -> Sequence[str]:
+        return ["fake"]
+
+    def search(self, source_id: str, topic: str, limit: int = 10) -> list[StubCandidate]:
+        self.calls.append((source_id, topic, limit))
+        return self.candidates[:limit]
+
+
+def run_search(
+    monkeypatch: pytest.MonkeyPatch,
+    capsys: pytest.CaptureFixture[str],
+    candidates: Sequence[StubCandidate],
+    *args: str,
+) -> tuple[int, dict[str, Any], StubRegistry]:
+    registry = StubRegistry(candidates)
+    monkeypatch.setattr(example, "default_registry", lambda: registry)
+    code = example.main(list(args))
+    captured = capsys.readouterr()
+    assert captured.err == ""
+    lines = [line for line in captured.out.splitlines() if line.strip()]
+    assert len(lines) == 1, captured.out
+    document = json.loads(lines[0])
+    assert isinstance(document, Mapping)
+    return code, document, registry
+
+
+BASE_ARGS = ("--topic", "red fox", "--format", "png", "--source", "fake")
+
+
+def test_png_candidate_is_kept_with_its_actual_dimensions(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    payload = png_payload(800, 600)
+    candidate = StubCandidate(
+        "fox",
+        "https://example.test/fox.png",
+        payload=payload,
+        # The source claims something else entirely; the bytes win.
+        mime_type="image/jpeg",
+        width=12,
+        height=12,
+    )
+
+    code, document, registry = run_search(
+        monkeypatch, capsys, [candidate], *BASE_ARGS, "--width", "640", "--height", "480"
+    )
+
+    assert code == envelope.EXIT_OK
+    assert document["status"] == envelope.STATUS_OK
+    assert document["error"] is None
+    item = document["items"][0]
+    assert item["source"] == "fake"
+    assert item["url"] == "https://example.test/fox.png"
+    assert item["format"] == "png"
+    assert (item["width"], item["height"]) == (800, 600)
+    assert item["size_bytes"] == len(payload)
+    assert candidate.fetch_calls == 1
+    # The bounded candidate window is requested from the source, not --count.
+    assert registry.calls == [("fake", "red fox", example.candidate_cap(10))]
+
+
+def test_ico_request_with_only_png_payloads_yields_no_format(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    candidates = [
+        StubCandidate("fox", "https://example.test/a.png", payload=png_payload(400, 400), mime_type="image/x-icon"),
+        StubCandidate("fox2", "https://example.test/b.png", payload=png_payload(500, 500), mime_type="image/ico"),
+    ]
+
+    code, document, _ = run_search(
+        monkeypatch,
+        capsys,
+        candidates,
+        "--topic",
+        "red fox",
+        "--format",
+        "ico",
+        "--source",
+        "fake",
+        "--width",
+        "64",
+        "--height",
+        "64",
+    )
+
+    assert code == envelope.EXIT_NO_FORMAT
+    assert document["status"] == envelope.STATUS_NO_FORMAT
+    assert document["items"] == []
+    assert document["error"]["code"] == "no_format_match"
+    assert document["error"]["details"]["requested_format"] == "ico"
+    assert document["error"]["details"]["unreadable_candidates"] == 0
+    assert document["error"]["details"]["format_matches"] == 0
+
+
+def test_ico_payload_is_kept_for_an_ico_request(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    candidate = StubCandidate("fox", "https://example.test/fox.ico", payload=ico_payload(64, 48))
+
+    code, document, _ = run_search(
+        monkeypatch,
+        capsys,
+        [candidate],
+        "--topic",
+        "red fox",
+        "--format",
+        "ico",
+        "--source",
+        "fake",
+        "--width",
+        "32",
+        "--height",
+        "32",
+    )
+
+    assert code == envelope.EXIT_OK
+    item = document["items"][0]
+    assert item["format"] == "ico"
+    assert (item["width"], item["height"]) == (64, 48)
+
+
+def test_all_too_small_payloads_yield_no_size(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    candidates = [
+        StubCandidate("small", "https://example.test/a.png", payload=png_payload(100, 100), width=4000, height=4000),
+        StubCandidate("tall", "https://example.test/b.png", payload=png_payload(900, 100)),
+    ]
+
+    code, document, _ = run_search(
+        monkeypatch, capsys, candidates, *BASE_ARGS, "--width", "200", "--height", "200"
+    )
+
+    assert code == envelope.EXIT_NO_SIZE
+    assert document["status"] == envelope.STATUS_NO_SIZE
+    assert document["items"] == []
+    assert document["error"]["code"] == "no_size_match"
+    assert document["error"]["details"]["format_matches"] == 2
+    assert document["error"]["details"]["unreadable_candidates"] == 0
+
+
+def test_exactly_minimum_size_is_accepted(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    candidate = StubCandidate("edge", "https://example.test/edge.png", payload=png_payload(200, 200))
+
+    code, document, _ = run_search(
+        monkeypatch, capsys, [candidate], *BASE_ARGS, "--width", "200", "--height", "200"
+    )
+
+    assert code == envelope.EXIT_OK
+    assert (document["items"][0]["width"], document["items"][0]["height"]) == (200, 200)
+
+
+def test_no_format_and_no_size_and_access_error_stay_distinct(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    format_code, format_document, _ = run_search(
+        monkeypatch,
+        capsys,
+        [StubCandidate("gif", "https://example.test/a.png", payload=gif_payload())],
+        *BASE_ARGS,
+    )
+    size_code, size_document, _ = run_search(
+        monkeypatch,
+        capsys,
+        [StubCandidate("small", "https://example.test/a.png", payload=png_payload(10, 10))],
+        *BASE_ARGS,
+        "--width",
+        "100",
+        "--height",
+        "100",
+    )
+    access_code, access_document, _ = run_search(
+        monkeypatch,
+        capsys,
+        [StubCandidate("broken", "https://example.test/a.png", error=SourceAccessError("refused"))],
+        *BASE_ARGS,
+    )
+
+    assert format_document["status"] == envelope.STATUS_NO_FORMAT
+    assert size_document["status"] == envelope.STATUS_NO_SIZE
+    assert access_document["status"] == envelope.STATUS_ACCESS_ERROR
+    assert len({format_code, size_code, access_code}) == 3
+    assert (format_code, size_code, access_code) == (
+        envelope.EXIT_NO_FORMAT,
+        envelope.EXIT_NO_SIZE,
+        envelope.EXIT_ACCESS_ERROR,
+    )
+
+
+def test_fetch_failure_yields_access_error(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    candidates = [
+        StubCandidate(
+            "broken",
+            "https://example.test/a.png",
+            error=SourceAccessError("image source returned HTTP status 503", url="https://example.test/a.png"),
+        )
+    ]
+
+    code, document, _ = run_search(monkeypatch, capsys, candidates, *BASE_ARGS)
+
+    assert code == envelope.EXIT_ACCESS_ERROR
+    assert document["status"] == envelope.STATUS_ACCESS_ERROR
+    assert document["items"] == []
+    assert document["error"]["code"] == "candidate_unreadable"
+    assert document["error"]["details"]["failures"][0]["url"] == "https://example.test/a.png"
+
+
+def test_non_image_payload_is_no_format_not_access_error(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    """Bytes that are no image at all are still "not the requested format".
+
+    A live source answers with HTML error pages, licence documents and vector
+    files; none of them is a png, so the topic verdict is ``no_format`` and the
+    caller must not see an access error (or a partial download) instead.
+    """
+
+    candidate = StubCandidate(
+        "junk", "https://example.test/a.png", payload=b"not-an-image", mime_type="image/png"
+    )
+
+    code, document, _ = run_search(monkeypatch, capsys, [candidate], *BASE_ARGS)
+
+    assert code == envelope.EXIT_NO_FORMAT
+    assert document["status"] == envelope.STATUS_NO_FORMAT
+    assert document["items"] == []
+    assert document["error"]["code"] == "no_format_match"
+    details = document["error"]["details"]
+    assert details["other_format_candidates"] == 1
+    assert details["observed_formats"] == {example.UNKNOWN_FORMAT: 1}
+    assert details["unreadable_candidates"] == 0
+
+
+def test_search_keeps_png_when_the_window_also_serves_other_formats(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    """The real source mixes formats; a working search stays ``ok``.
+
+    Every non-png payload in the bounded window used to be classified as an
+    unreadable candidate, which demoted a successful search to
+    ``partial_download`` (exit 6).  They are format mismatches now.
+    """
+
+    candidates = [
+        StubCandidate("gif", "https://example.test/a.gif", payload=gif_payload(), mime_type="image/png"),
+        StubCandidate("jpeg", "https://example.test/a.jpg", payload=jpeg_payload(), mime_type="image/png"),
+        StubCandidate("svg", "https://example.test/a.svg", payload=svg_payload(), mime_type="image/png"),
+        StubCandidate("tiff", "https://example.test/a.tiff", payload=tiff_payload(), mime_type="image/png"),
+        StubCandidate("pdf", "https://example.test/a.pdf", payload=pdf_payload(), mime_type="image/png"),
+        StubCandidate("page", "https://example.test/a.html", payload=b"<html>rate limited</html>"),
+        StubCandidate("fox", "https://example.test/fox.png", payload=png_payload(800, 600)),
+    ]
+
+    code, document, _ = run_search(
+        monkeypatch, capsys, candidates, *BASE_ARGS, "--width", "640", "--height", "480"
+    )
+
+    assert code == envelope.EXIT_OK
+    assert document["status"] == envelope.STATUS_OK
+    assert document["error"] is None
+    assert [item["url"] for item in document["items"]] == ["https://example.test/fox.png"]
+    assert (document["items"][0]["width"], document["items"][0]["height"]) == (800, 600)
+
+
+def test_unfetchable_candidate_does_not_demote_a_usable_search(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    """A working search stays ``ok`` even when one candidate cannot be fetched."""
+
+    candidates = [
+        StubCandidate(
+            "missing",
+            "https://example.test/missing.png",
+            error=SourceAccessError("image source returned HTTP status 503"),
+        ),
+        StubCandidate("fox", "https://example.test/fox.png", payload=png_payload(300, 200)),
+    ]
+
+    code, document, _ = run_search(
+        monkeypatch, capsys, candidates, *BASE_ARGS, "--width", "100", "--height", "100"
+    )
+
+    assert code == envelope.EXIT_OK
+    assert document["status"] == envelope.STATUS_OK
+    assert [item["url"] for item in document["items"]] == ["https://example.test/fox.png"]
+
+
+def test_ico_request_with_only_foreign_formats_yields_no_format_not_access_error(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    """REQ-007: ico may be unavailable, and that is ``no_format`` (exit 3)."""
+
+    candidates = [
+        StubCandidate("gif", "https://example.test/a.gif", payload=gif_payload()),
+        StubCandidate("jpeg", "https://example.test/a.jpg", payload=jpeg_payload()),
+        StubCandidate("svg", "https://example.test/a.svg", payload=svg_payload()),
+        StubCandidate("tiff", "https://example.test/a.tiff", payload=tiff_payload()),
+        StubCandidate("page", "https://example.test/a.html", payload=b"<html></html>"),
+    ]
+
+    code, document, _ = run_search(
+        monkeypatch,
+        capsys,
+        candidates,
+        "--topic",
+        "red fox",
+        "--format",
+        "ico",
+        "--source",
+        "fake",
+        "--width",
+        "64",
+        "--height",
+        "64",
+    )
+
+    assert code == envelope.EXIT_NO_FORMAT
+    assert document["status"] == envelope.STATUS_NO_FORMAT
+    details = document["error"]["details"]
+    assert details["requested_format"] == "ico"
+    assert details["other_format_candidates"] == 5
+    assert details["observed_formats"] == {
+        "gif": 1,
+        "jpeg": 1,
+        "svg": 1,
+        "tiff": 1,
+        example.UNKNOWN_FORMAT: 1,
+    }
+    assert details["unreadable_candidates"] == 0
+
+
+def test_no_size_survives_other_formats_in_the_same_window(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    """REQ-008: format-matching but too-small images keep their own status."""
+
+    candidates = [
+        StubCandidate("gif", "https://example.test/a.gif", payload=gif_payload()),
+        StubCandidate("small", "https://example.test/a.png", payload=png_payload(100, 100)),
+        StubCandidate("svg", "https://example.test/a.svg", payload=svg_payload()),
+    ]
+
+    code, document, _ = run_search(
+        monkeypatch, capsys, candidates, *BASE_ARGS, "--width", "200", "--height", "200"
+    )
+
+    assert code == envelope.EXIT_NO_SIZE
+    assert document["status"] == envelope.STATUS_NO_SIZE
+    details = document["error"]["details"]
+    assert details["format_matches"] == 1
+    assert details["other_format_candidates"] == 2
+    assert details["unreadable_candidates"] == 0
+
+
+def test_corrupt_payload_of_the_requested_format_does_not_hide_a_valid_match(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    corrupt = images.PNG_SIGNATURE + struct.pack(">I", 13) + b"IDAT" + b"\x00" * 13
+    candidates = [
+        StubCandidate("broken", "https://example.test/broken.png", payload=corrupt),
+        StubCandidate("fox", "https://example.test/fox.png", payload=png_payload(200, 200)),
+    ]
+
+    code, document, _ = run_search(
+        monkeypatch, capsys, candidates, *BASE_ARGS, "--width", "100", "--height", "100"
+    )
+
+    assert code == envelope.EXIT_OK
+    assert document["status"] == envelope.STATUS_OK
+    assert [item["url"] for item in document["items"]] == ["https://example.test/fox.png"]
+
+
+def test_empty_search_window_is_no_format_not_access_error(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    code, document, _ = run_search(monkeypatch, capsys, [], *BASE_ARGS)
+
+    assert code == envelope.EXIT_NO_FORMAT
+    assert document["status"] == envelope.STATUS_NO_FORMAT
+    assert document["error"]["details"]["candidate_count"] == 0
+    assert document["error"]["details"]["unreadable_candidates"] == 0
+
+
+def test_candidate_window_is_bounded_by_the_requested_count(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    candidates = [
+        StubCandidate(f"fox{n}", f"https://example.test/{n}.png", payload=png_payload(100, 100))
+        for n in range(40)
+    ]
+
+    code, document, registry = run_search(
+        monkeypatch, capsys, candidates, *BASE_ARGS, "--count", "3"
+    )
+
+    assert code == envelope.EXIT_OK
+    assert len(document["items"]) == 3
+    assert registry.calls == [("fake", "red fox", example.candidate_cap(3))]
+    assert example.candidate_cap(3) == 12
+    # Fetching stops as soon as enough usable images were found.
+    assert sum(candidate.fetch_calls for candidate in candidates) == 3
+
+
+def test_filtering_walks_past_rejected_candidates_until_the_count_is_met(
+    monkeypatch: pytest.MonkeyPatch, capsys: pytest.CaptureFixture[str]
+) -> None:
+    candidates = [
+        StubCandidate("gif", "https://example.test/0.png", payload=gif_payload()),
+        StubCandidate("tiny", "https://example.test/1.png", payload=png_payload(10, 10)),
+        StubCandidate("ok1", "https://example.test/2.png", payload=png_payload(120, 120)),
+        StubCandidate("ok2", "https://example.test/3.png", payload=png_payload(130, 130)),
+        StubCandidate("never", "https://example.test/4.png", payload=png_payload(140, 140)),
+    ]
+
+    code, document, _ = run_search(
+        monkeypatch, capsys, candidates, *BASE_ARGS, "--count", "2", "--width", "100", "--height", "100"
+    )
+
+    assert code == envelope.EXIT_OK
+    assert [item["url"] for item in document["items"]] == [
+        "https://example.test/2.png",
+        "https://example.test/3.png",
+    ]
+    assert [(item["width"], item["height"]) for item in document["items"]] == [(120, 120), (130, 130)]
+    assert candidates[-1].fetch_calls == 0