TDD Assessment

What changed

• New flatten() function: replaces newlines with spaces, no truncation.
• runThread text output path switched from truncate(text, 80) to flatten(text).

flatten() unit tests — adequate

TestFlatten covers the cases that matter:

• No newlines (passthrough)
• Single newline
• Multiple newlines
• Empty string
• Long string preserved (the key behavioral difference from truncate)
• Long string with newlines preserved

No gaps here. The only minor omission is a \r\n (Windows-style) input case, but Slack's API does not produce \r\n in message text, so this is not worth adding.

Integration-level test for runThread text output — gap exists

TestRunThread_Success exercises the text output path but does not assert on what was printed. It only asserts require.NoError. This means:

• A regression that silently truncates output again (e.g. accidentally reverting to truncate) would not be caught by any test.
• A message with embedded newlines going through flatten is never verified end-to-end.

The JSON path already has output-capture tests (TestRunThread_JSONIncludesReactions, TestRunThread_JSONIncludesFiles). The text path has no equivalent.

Suggested addition (not blocking, but worth a follow-up issue):

func TestRunThread_TextOutput_MultilineMessage(t *testing.T) {
    server := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
        switch r.URL.Path {
        case "/conversations.replies":
            _ = json.NewEncoder(w).Encode(map[string]interface{}{
                "ok": true,
                "messages": []map[string]interface{}{
                    {"ts": "1234567890.123456", "user": "U001", "text": "Line one\nLine two\nLine three that is quite long and should not be truncated"},
                },
            })
        case "/users.info":
            mockUserInfoHandler(w, r)
        }
    }))
    defer server.Close()

    c := client.NewWithConfig(server.URL, "test-token", nil)
    opts := &threadOptions{limit: 100}

    var buf strings.Builder
    output.Writer = &buf
    defer func() { output.Writer = os.Stdout }()

    err := runThread("C123", "1234567890.123456", opts, c)
    require.NoError(t, err)

    got := buf.String()
    assert.Contains(t, got, "Line one Line two Line three that is quite long and should not be truncated")
    assert.NotContains(t, got, "...", "thread text should not be truncated")
}

Summary

The flatten() function itself is correct and well-tested. The one actionable gap is the lack of output assertions in TestRunThread_Success for the text path.