Fix for tox 4.15

tox.ini

@@ -3,10 +3,10 @@ isolated_build = true
 envlist =
     clear-coverage
     quality
-    py37-tox{3,4}
-    py38-tox{3,4}
-    py39-tox{3,4}
-    py310-tox{3,4}
+    py37-tox{3,414,4}
+    py38-tox{3,414,4}
+    py39-tox{3,414,4}
+    py310-tox{3,414,4}
     compute-coverage
 skip_missing_interpreters = true
 
@@ -17,6 +17,7 @@ setenv =
 deps =
     coverage
     tox3: tox == 3.*
+    tox414: tox == 4.*,<4.15
     tox4: tox == 4.*
 commands =
     coverage run --parallel-mode --include=tox_ipdb.py,tests.py --branch -m unittest {posargs:discover}
@@ -30,10 +31,10 @@ commands =
 
 [testenv:compute-coverage]
 depends =
-    py37-tox{3,4}
-    py38-tox{3,4}
-    py39-tox{3,4}
-    py310-tox{3,4}
+    py37-tox{3,414,4}
+    py38-tox{3,414,4}
+    py39-tox{3,414,4}
+    py310-tox{3,414,4}
 # Use single virtualenv for both coverage envs.
 envdir = {toxworkdir}/coverage
 parallel_show_output = true

tox_ipdb.py

@@ -59,7 +59,11 @@ def tox_add_env_config(env_conf: EnvConfigSet, state: State) -> None:
         _LOGGER.debug("tox-ipdb-plugin[%s]: New deps: %s", env_conf.name, new_deps)
 
         override = Override('{}.deps={}'.format(env_conf.name, '\n'.join(new_deps)))
-        env_conf.loaders[0].overrides[override.key] = override
+        # API changed in tox 4.15.0
+        if LooseVersion(tox.__version__) < LooseVersion('4.15.0'):
+            env_conf.loaders[0].overrides[override.key] = override  # type: ignore[assignment]
+        else:
+            env_conf.loaders[0].overrides.setdefault(override.key, []).append(override)
 
         # Clear cache
         env_conf._defined['deps']._cache = _PLACE_HOLDER  # type: ignore[attr-defined]  # _cache is not public API