tests: Add regression for v1.13.1 pane spacing issue

tests/fixtures/regressions/issue_800_default_size_many_windows.yaml

@@ -0,0 +1,12 @@
+session_name: many-windows-issue
+windows:
+- window_name: moo
+  layout: main-horizontal
+  panes:
+  - echo hello
+  - echo hello
+  - echo hello
+  - echo hello
+  - echo hello
+  - echo hello
+  - echo hello

tests/test_workspacebuilder.py

@@ -3,22 +3,26 @@
 import pathlib
 import textwrap
 import time
+import typing as t
 
 import pytest
 
 import kaptan
 
 import libtmux
-from libtmux import Window
 from libtmux.common import has_gte_version, has_lt_version
 from libtmux.test import retry_until, temp_session
+from libtmux.window import Window
 from tmuxp import config, exc
 from tmuxp.cli.load import load_plugins
 from tmuxp.workspacebuilder import WorkspaceBuilder
 
 from .constants import EXAMPLE_PATH, FIXTURE_PATH
 from .fixtures import utils as test_utils
 
+if t.TYPE_CHECKING:
+    from libtmux.server import Server
+
 
 def test_split_windows(session):
     yaml_config = test_utils.read_config_file("workspacebuilder/two_pane.yaml")
@@ -1217,3 +1221,40 @@ def is_almost_equal(x, y):
 
     assert is_almost_equal(height(panes[0]), height(panes[1]))
     assert is_almost_equal(width(panes[0]), width(panes[1]))
+
+
+def test_issue_800_default_size_many_windows(
+    server: "Server", monkeypatch: pytest.MonkeyPatch
+) -> None:
+    """Recreate default-size issue.
+
+    v1.13.1 added a default-size, but this can break building workspaces with
+    a lot of panes.
+
+    See also: https://github.com/tmux-python/tmuxp/issues/800
+    """
+    yaml_config = test_utils.read_config_file(
+        "regressions/issue_800_default_size_many_windows.yaml"
+    )
+    sconfig = kaptan.Kaptan(handler="yaml")
+    sconfig = sconfig.import_config(yaml_config).get()
+    sconfig = config.expand(sconfig)
+    sconfig = config.trickle(sconfig)
+
+    builder = WorkspaceBuilder(sconf=sconfig, server=server)
+
+    with pytest.raises(libtmux.exc.LibTmuxException, match="no space for new pane"):
+        builder.build()
+
+    assert len(server.list_sessions()) == 1
+
+    # Assign an active pane to the session
+    second_session = server.list_sessions()[0]
+    first_pane_on_second_session_id = second_session.list_windows()[0].list_panes()[0][
+        "pane_id"
+    ]
+    monkeypatch.setenv("TMUX_PANE", first_pane_on_second_session_id)
+
+    builder = WorkspaceBuilder(sconf=sconfig, server=server)
+
+    assert builder.find_current_attached_session() == second_session