test: add snapshot lifecycle, alias, and cross-db test cases (#47840)

## Summary

- Add 15 new test cases for snapshot feature covering lifecycle edge
cases, alias support, and cross-database restore
- Verify fix for #47578 (DropSnapshot during active restore)
- All tests verified on latest master image
(`master-20260224-091b147e-amd64`)

### New Test Classes

| Class | Tests | Level | Description |
|-------|-------|-------|-------------|
| `TestMilvusClientSnapshotDropInvalid` | +1 | L1 | Drop during active
restore (#47578) |
| `TestMilvusClientSnapshotLifecycle` | +8 | L2/L3 | Collection
lifecycle + snapshot interactions |
| `TestMilvusClientSnapshotAlias` | +6 | L2 | Snapshot ops via
collection aliases |

### Test Details

**Lifecycle tests (L2):**
- Drop target collection during restore
- Rename source collection after snapshot creation
- Create snapshot on collection being restored to
- Restore failure leaves no resource leak
- Concurrent drop of same snapshot (idempotent)
- Create snapshot during drop of source collection
- Cross-database snapshot restore
- Drop and restore race condition (L3)

**Alias tests (L2):**
- Create snapshot via alias → describe shows real collection name
- List snapshots via alias == list via real name
- Restore from alias-created snapshot with data integrity
- List restore jobs via alias on restored collection
- Dropped alias → create snapshot fails with "not found"
- Alter alias retarget → list snapshots reflects new target

## Test plan

- [x] All 14 L1/L2 tests pass on standalone
(master-20260224-091b147e-amd64)
- [x] L3 race test works but may timeout on standalone due to resource
exhaustion

---------

Signed-off-by: zhuwenxing <wenxing.zhu@zilliz.com>
Co-authored-by: Claude Opus 4.7 <noreply@anthropic.com>

tests/Makefile

@@ -0,0 +1,95 @@
+# tests/Makefile — lint helpers for Python files under tests/.
+#
+# All targets operate on the *PR-changed* set: files under tests/**/*.py that
+# differ between $(BASE_REF) and HEAD (three-dot diff = since merge-base),
+# matching the GitHub Actions "Python Lint (tests/)" workflow.
+#
+# Usage (run from this tests/ directory):
+#   make lint          # ruff check          (CI equivalent)
+#   make format-check  # ruff format --check (CI equivalent)
+#   make ci            # lint + format-check
+#   make lint-fix      # ruff check --fix
+#   make format        # ruff format
+#
+# Variables:
+#   BASE_REF      diff base ref. Auto-detected from the current branch's open PR
+#                 via `gh pr view`. If no PR exists, you MUST set it explicitly,
+#                 e.g.: make ci BASE_REF=origin/master
+#   RUFF_VERSION  ruff version (default: 0.15.11, pinned to .github/workflows/python-lint.yaml)
+#
+# Requires `uvx` (ships with `uv`). Ruff is fetched & cached on first run.
+# Auto-detection requires `gh` authenticated (`gh auth status`).
+
+RUFF_VERSION ?= 0.15.11
+RUFF         := uvx ruff@$(RUFF_VERSION)
+REPO_ROOT    := $(shell git rev-parse --show-toplevel)
+
+# Auto-detect the base ref from the current branch's open PR.
+# Steps:
+#   1. Read the PR URL (always lives under the base repo) and base branch via gh.
+#      Extract base repo as "<owner>/<name>" from the URL path.
+#   2. Find which local remote points to that base repo (must NOT assume "origin"
+#      — for forks, "upstream" is typically the base; for direct clones, "origin").
+#   3. Emit "<remote>/<baseRefName>".
+# Empty when no PR exists, no remote matches, or gh is unauthenticated —
+# user must then set BASE_REF explicitly.
+BASE_REF ?= $(shell \
+  pr_url=$$(gh pr view --json url -q .url 2>/dev/null); \
+  base_branch=$$(gh pr view --json baseRefName -q .baseRefName 2>/dev/null); \
+  if [ -z "$$pr_url" ] || [ -z "$$base_branch" ]; then exit 0; fi; \
+  base_repo=$$(echo "$$pr_url" | sed -E 's|^https?://[^/]+/([^/]+/[^/]+)/.*|\1|'); \
+  if [ -z "$$base_repo" ]; then exit 0; fi; \
+  remote=$$(git -C $(REPO_ROOT) remote -v | awk -v p="$$base_repo" 'index($$2, p) > 0 && $$3=="(fetch)" {print $$1; exit}'); \
+  if [ -z "$$remote" ]; then exit 0; fi; \
+  echo "$$remote/$$base_branch")
+
+CHANGED_FILES_CMD = git -C $(REPO_ROOT) diff --name-only --diff-filter=ACMR $(BASE_REF)...HEAD -- 'tests/**/*.py'
+
+.PHONY: help lint format-check ci lint-fix format _require-base-ref
+
+help:
+	@echo "tests/ Makefile — lint PR-changed *.py using ruff $(RUFF_VERSION)"
+	@echo
+	@echo "Targets:"
+	@echo "  make lint          ruff check          (CI equivalent)"
+	@echo "  make format-check  ruff format --check (CI equivalent)"
+	@echo "  make ci            lint + format-check"
+	@echo "  make lint-fix      ruff check --fix"
+	@echo "  make format        ruff format"
+	@echo
+	@echo "BASE_REF: auto-detected from the current branch's open PR via 'gh pr view'."
+	@echo "          When no PR exists, you must set it explicitly:"
+	@echo "            make ci BASE_REF=origin/master"
+	@if [ -n "$(BASE_REF)" ]; then echo; echo "Currently detected: BASE_REF=$(BASE_REF)"; \
+	else echo; echo "Currently: BASE_REF is unset (no open PR detected)."; fi
+
+_require-base-ref:
+	@if [ -z "$(BASE_REF)" ]; then \
+	  echo "Error: BASE_REF is not set."; \
+	  echo "       No open PR detected for the current branch via 'gh pr view'."; \
+	  echo "       Set it explicitly, e.g.:"; \
+	  echo "         make $(or $(MAKECMDGOALS),ci) BASE_REF=origin/master"; \
+	  exit 1; \
+	fi
+
+lint: _require-base-ref
+	@files=$$($(CHANGED_FILES_CMD)); \
+	if [ -z "$$files" ]; then echo "No changed Python files under tests/ (base: $(BASE_REF))."; \
+	else cd $(REPO_ROOT) && $(RUFF) check $$files; fi
+
+format-check: _require-base-ref
+	@files=$$($(CHANGED_FILES_CMD)); \
+	if [ -z "$$files" ]; then echo "No changed Python files under tests/ (base: $(BASE_REF))."; \
+	else cd $(REPO_ROOT) && $(RUFF) format --check --diff $$files; fi
+
+ci: lint format-check
+
+lint-fix: _require-base-ref
+	@files=$$($(CHANGED_FILES_CMD)); \
+	if [ -z "$$files" ]; then echo "No changed Python files under tests/ (base: $(BASE_REF))."; \
+	else cd $(REPO_ROOT) && $(RUFF) check --fix $$files; fi
+
+format: _require-base-ref
+	@files=$$($(CHANGED_FILES_CMD)); \
+	if [ -z "$$files" ]; then echo "No changed Python files under tests/ (base: $(BASE_REF))."; \
+	else cd $(REPO_ROOT) && $(RUFF) format $$files; fi

tests/README.md

@@ -108,3 +108,38 @@ $ uv run ruff format --check .  # format check only (CI-friendly)
 
 Rules enabled: `E`, `F`, `W`, `I`, `UP`. Target Python version: `3.10`.
 
+#### Lint only PR-changed files (Python Lint CI parity)
+
+The GitHub Actions workflow `.github/workflows/python-lint.yaml` (job
+**"Python Lint (tests/) / Ruff (changed files only)"**) runs `ruff check`
+and `ruff format --check` against the *changed* `tests/**/*.py` set on
+every PR. Running `uv run ruff check .` over the whole tree is too coarse
+because the historical contents of many files predate the lint config and
+will fail unrelated rules.
+
+To reproduce the CI step locally, use the `Makefile` shipped in this directory:
+
+```shell
+$ cd tests/
+$ make ci             # ruff check + format --check on PR-changed *.py (CI equivalent)
+$ make lint-fix       # ruff check --fix on PR-changed *.py
+$ make format         # ruff format on PR-changed *.py
+$ make help           # show all targets and the detected BASE_REF
+```
+
+`BASE_REF` is auto-detected from the current branch's open PR via `gh pr view`:
+the PR URL is parsed to discover the base `<owner>/<repo>` and matched against
+your local git remotes, producing e.g. `upstream/master`, `upstream/2.x`, or
+`origin/main` for direct clones.
+
+If no open PR exists for the branch, you **must** set `BASE_REF` explicitly
+(no guessing — a wrong base diffs against unrelated commits):
+
+```shell
+$ make ci BASE_REF=upstream/master
+```
+
+Requires `uv` (provides `uvx`) and `gh` authenticated against GitHub
+(`gh auth status`). The ruff version is pinned in the `Makefile` via
+`RUFF_VERSION` to match the workflow.
+

tests/README_CN.md

@@ -108,3 +108,37 @@ $ uv run ruff format --check .  # 只检查不修改 (CI 友好)
 
 启用的规则：`E`、`F`、`W`、`I`、`UP`；目标 Python 版本：`3.10`。
 
+#### 仅检查 PR 修改的文件 (与 Python Lint CI 一致)
+
+GitHub Actions workflow `.github/workflows/python-lint.yaml`
+（job **"Python Lint (tests/) / Ruff (changed files only)"**）
+只对 PR 修改的 `tests/**/*.py` 文件跑 `ruff check` 和 `ruff format --check`。
+直接对整个 `tests/` 目录执行 `uv run ruff check .` 太粗——很多历史文件早于
+当前 lint 配置，会因为无关规则失败。
+
+要在本地复现 CI 这一步，使用本目录下的 `Makefile`：
+
+```shell
+$ cd tests/
+$ make ci             # 对 PR 修改文件跑 ruff check + format --check（与 CI 等价）
+$ make lint-fix       # 对 PR 修改文件跑 ruff check --fix
+$ make format         # 对 PR 修改文件跑 ruff format
+$ make help           # 显示所有 target 以及当前自动检测到的 BASE_REF
+```
+
+`BASE_REF` 通过 `gh pr view` 从当前分支的开放 PR 中自动检测：
+解析 PR URL 得到 base `<owner>/<repo>`，再匹配本地 git remotes，
+得到形如 `upstream/master`、`upstream/2.x` 或（直接 clone 主仓库时的）
+`origin/main`。
+
+如果当前分支没有开放 PR，**必须**显式设置 `BASE_REF`
+（不再做猜测——base 选错会 diff 出无关 commit）：
+
+```shell
+$ make ci BASE_REF=upstream/master
+```
+
+需要本地已安装 `uv`（提供 `uvx`）和已认证的 `gh`
+（`gh auth status`）。Makefile 通过 `RUFF_VERSION` 锁定与
+workflow 一致的 ruff 版本。
+