textual/tests/snapshot_tests/conftest.py

from __future__ import annotations

import difflib
import os
from dataclasses import dataclass
from datetime import datetime
from operator import attrgetter
from os import PathLike
from pathlib import Path
from typing import Union, List, Optional, Callable, Iterable

import pytest
from _pytest.config import ExitCode
from _pytest.fixtures import FixtureRequest
from _pytest.main import Session
from _pytest.terminal import TerminalReporter
from jinja2 import Template
from rich.console import Console
from syrupy import SnapshotAssertion

from textual._doc import take_svg_screenshot
from textual._import_app import import_app
from textual.app import App

TEXTUAL_SNAPSHOT_SVG_KEY = pytest.StashKey[str]()
TEXTUAL_ACTUAL_SVG_KEY = pytest.StashKey[str]()
TEXTUAL_SNAPSHOT_PASS = pytest.StashKey[bool]()
TEXTUAL_APP_KEY = pytest.StashKey[App]()


@pytest.fixture
def snap_compare(
    snapshot: SnapshotAssertion, request: FixtureRequest
) -> Callable[[str], bool]:
    """
    This fixture returns a function which can be used to compare the output of a Textual
    app with the output of the same app in the past. This is snapshot testing, and it
    used to catch regressions in output.
    """

    def compare(
        app_path: str,
        press: Iterable[str] = ("_",),
        terminal_size: tuple[int, int] = (24, 80),
    ) -> bool:
        """
        Compare a current screenshot of the app running at app_path, with
        a previously accepted (validated by human) snapshot stored on disk.
        When the `--snapshot-update` flag is supplied (provided by syrupy),
        the snapshot on disk will be updated to match the current screenshot.

        Args:
            app_path (str): The path of the app.
            press (Iterable[str]): Key presses to run before taking screenshot. "_" is a short pause.
            terminal_size (tuple[int, int]): A pair of integers (rows, columns), representing terminal size.

        Returns:
            bool: True if the screenshot matches the snapshot.
        """
        node = request.node
        app = import_app(app_path)
        actual_screenshot = take_svg_screenshot(
            app=app,
            press=press,
            terminal_size=terminal_size,
        )
        result = snapshot == actual_screenshot

        if result is False:
            # The split and join below is a mad hack, sorry...
            node.stash[TEXTUAL_SNAPSHOT_SVG_KEY] = "\n".join(str(snapshot).splitlines()[1:-1])
            node.stash[TEXTUAL_ACTUAL_SVG_KEY] = actual_screenshot
            node.stash[TEXTUAL_APP_KEY] = app
        else:
            node.stash[TEXTUAL_SNAPSHOT_PASS] = True

        return result

    return compare


@dataclass
class SvgSnapshotDiff:
    """Model representing a diff between current screenshot of an app,
    and the snapshot on disk. This is ultimately intended to be used in
    a Jinja2 template."""
    snapshot: Optional[str]
    actual: Optional[str]
    test_name: str
    file_similarity: float
    path: PathLike
    line_number: int
    app: App
    environment: dict


def pytest_sessionfinish(
    session: Session,
    exitstatus: Union[int, ExitCode],
) -> None:
    """Called after whole test run finished, right before returning the exit status to the system.
    Generates the snapshot report and writes it to disk.
    """
    diffs: List[SvgSnapshotDiff] = []
    num_snapshots_passing = 0
    for item in session.items:

        # Grab the data our fixture attached to the pytest node
        num_snapshots_passing += int(item.stash.get(TEXTUAL_SNAPSHOT_PASS, False))
        snapshot_svg = item.stash.get(TEXTUAL_SNAPSHOT_SVG_KEY, None)
        actual_svg = item.stash.get(TEXTUAL_ACTUAL_SVG_KEY, None)
        app = item.stash.get(TEXTUAL_APP_KEY, None)

        if snapshot_svg and actual_svg and app:
            path, line_index, name = item.reportinfo()
            diffs.append(
                SvgSnapshotDiff(
                    snapshot=str(snapshot_svg),
                    actual=str(actual_svg),
                    file_similarity=100
                                    * difflib.SequenceMatcher(
                        a=str(snapshot_svg), b=str(actual_svg)
                    ).ratio(),
                    test_name=name,
                    path=path,
                    line_number=line_index + 1,
                    app=app,
                    environment=dict(os.environ),
                )
            )

    if diffs:
        diff_sort_key = attrgetter("file_similarity")
        diffs = sorted(diffs, key=diff_sort_key)

        conftest_path = Path(__file__)
        snapshot_template_path = (
            conftest_path.parent / "snapshot_report_template.jinja2"
        )
        snapshot_report_path_dir = conftest_path.parent / "output"
        snapshot_report_path_dir.mkdir(parents=True, exist_ok=True)
        snapshot_report_path = snapshot_report_path_dir / "snapshot_report.html"

        template = Template(snapshot_template_path.read_text())

        num_fails = len(diffs)
        num_snapshot_tests = len(diffs) + num_snapshots_passing

        rendered_report = template.render(
            diffs=diffs,
            passes=num_snapshots_passing,
            fails=num_fails,
            pass_percentage=100 * (num_snapshots_passing / max(num_snapshot_tests, 1)),
            fail_percentage=100 * (num_fails / max(num_snapshot_tests, 1)),
            num_snapshot_tests=num_snapshot_tests,
            now=datetime.utcnow(),
        )
        with open(snapshot_report_path, "w+", encoding="utf-8") as snapshot_file:
            snapshot_file.write(rendered_report)

        session.config._textual_snapshots = diffs
        session.config._textual_snapshot_html_report = snapshot_report_path


def pytest_terminal_summary(
    terminalreporter: TerminalReporter,
    exitstatus: ExitCode,
    config: pytest.Config,
) -> None:
    """Add a section to terminal summary reporting.
    Displays the link to the snapshot report that was generated in a prior hook.
    """
    diffs = getattr(config, "_textual_snapshots", None)
    console = Console()
    if diffs:
        snapshot_report_location = config._textual_snapshot_html_report
        console.rule("[b red]Textual Snapshot Report", style="red")
        console.print(f"\n[black on red]{len(diffs)} mismatched snapshots[/]\n"
                      f"\n[b]View the [link=file://{snapshot_report_location}]failure report[/].\n")
        console.print(f"[dim]{snapshot_report_location}\n")
        console.rule(style="red")