test: mock network calls in altair chart dataframe tests

[mscolnick]

No description provided.

[vercel]

The latest updates on your projects. Learn more about Vercel for GitHub.

Project	Deployment	Actions	Updated (UTC)
marimo-docs	Ready	Preview, Comment	Jul 15, 2026 6:16pm

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

[cubic-dev-ai]

1 issue found across 1 file

Prompt for AI agents (unresolved issues)

Check if these issues are valid — if so, understand the root cause of each and fix them. If appropriate, use sub-agents to investigate and fix each issue separately.


<file name="tests/_plugins/ui/_impl/test_altair_chart.py">

<violation number="1" location="tests/_plugins/ui/_impl/test_altair_chart.py:780">
P1: The `unittest.mock.patch("urllib.request.urlopen", ...)` in `test_get_dataframe_csv()` does not intercept the actual network call. When the chart data URL ends with `.csv`, the implementation in `_get_dataframe_from_chart` calls `pl.read_csv(url)` (or `pd.read_csv(url)`), both of which handle HTTP natively — they do **not** use `urllib.request.urlopen`. The mock is a no-op, so the test still makes a real HTTP request to the CDN.

This means the test (1) depends on external network availability, (2) will fail in airgapped or offline environments, and (3) defeats the PR's goal of mocking network calls.

To fix, either use a local file path or CSV string instead of a URL, or patch `polars.read_csv` / `pandas.read_csv` directly depending on which library the test environment provides.</violation>
</file>

Architecture diagram

sequenceDiagram
    participant Test as Test Function
    participant Mock as unittest.mock.patch
    participant URL as urllib.request.urlopen
    participant Chart as altair_chart()
    participant DF as DataFrame (pd/pl)

    Note over Test,DF: Mocked Network Call Flow
    Test->>Mock: patch("urllib.request.urlopen", ...)
    Mock-->>URL: replace with io.BytesIO(fake_payload)
    Test->>Chart: altair_chart(alt.Chart(data).mark_point()...)
    Chart->>URL: fetch data from URL (e.g., stocks.csv)
    URL-->>Chart: return fake_payload bytes
    Chart->>Chart: parse CSV/JSON into DataFrame
    Chart-->>Test: chart.dataframe
    Test->>Test: assert isinstance(df, pd.DataFrame or pl.DataFrame)

Loading

<sub>Reply with feedback, questions, or to request a fix.

Re-trigger cubic</sub>

[cubic-dev-ai]

P1: The unittest.mock.patch("urllib.request.urlopen", ...) in test_get_dataframe_csv() does not intercept the actual network call. When the chart data URL ends with .csv, the implementation in _get_dataframe_from_chart calls pl.read_csv(url) (or pd.read_csv(url)), both of which handle HTTP natively — they do not use urllib.request.urlopen. The mock is a no-op, so the test still makes a real HTTP request to the CDN.

This means the test (1) depends on external network availability, (2) will fail in airgapped or offline environments, and (3) defeats the PR's goal of mocking network calls.

To fix, either use a local file path or CSV string instead of a URL, or patch polars.read_csv / pandas.read_csv directly depending on which library the test environment provides.

Prompt for AI agents

Check if this issue is valid — if so, understand the root cause and fix it. At tests/_plugins/ui/_impl/test_altair_chart.py, line 780:

<comment>The `unittest.mock.patch("urllib.request.urlopen", ...)` in `test_get_dataframe_csv()` does not intercept the actual network call. When the chart data URL ends with `.csv`, the implementation in `_get_dataframe_from_chart` calls `pl.read_csv(url)` (or `pd.read_csv(url)`), both of which handle HTTP natively — they do **not** use `urllib.request.urlopen`. The mock is a no-op, so the test still makes a real HTTP request to the CDN.

This means the test (1) depends on external network availability, (2) will fail in airgapped or offline environments, and (3) defeats the PR's goal of mocking network calls.

To fix, either use a local file path or CSV string instead of a URL, or patch `polars.read_csv` / `pandas.read_csv` directly depending on which library the test environment provides.</comment>

<file context>
@@ -777,8 +777,13 @@ def test_get_dataframe_csv() -> None:
     data = "https://cdn.jsdelivr.net/npm/vega-datasets@v1.29.0/data/stocks.csv"
-    chart = altair_chart(alt.Chart(data).mark_point().encode(x="values:Q"))
-    assert isinstance(chart.dataframe, (pd.DataFrame, pl.DataFrame))
+    fake_payload = b"symbol,price\nMSFT,39.81\nAAPL,28.13\n"
+    with unittest.mock.patch(
+        "urllib.request.urlopen",
</file context>

[github-actions]

🚀 Development release published. You may be able to view the changes at https://marimo.app?v=0.23.15-dev24