regrun 0.4.0

YAML-driven regression test runner for HTTP APIs, MCP servers, and shell commands

regrun

Deterministic YAML-driven regression test runner for APIs, MCP servers, and WebSocket streams.

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What is regrun?

regrun lets you define regression tests as YAML files and run them against live services — no test framework required. You describe what to call, what to assert, and what to capture; regrun handles execution, variable interpolation, and reporting. It supports four runners: REST APIs (httpx), MCP tools (fastmcp CLI), shell commands (bash), and WebSocket streams (websocket). Tests share a variable store across files, so a JWT captured in setup is available to every subsequent test without any wiring.

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Installation

pip install regrun

Requires Python 3.12 or later.

The MCP runner requires uvx and the fastmcp CLI available on PATH:

pip install fastmcp

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Quick Start

Create two test files for a fictional myapp running at http://localhost:8000.

tests/regression/00_setup.yaml — acquire a JWT:

meta:
  product: myapp
  layer: setup
  runner: httpx
  endpoint: "http://localhost:8000"

variables:
  RUN_ID: "{{timestamp}}"
  TEST_EMAIL: "regtest-{{RUN_ID}}@example.com"
  TEST_PASSWORD: "TestPass123!"

groups:
  - id: 1
    name: "Auth"
    priority: high
    tests:
      - id: "S.1"
        name: "Login and capture JWT"
        method: POST
        path: "/api/v1/auth/login"
        auth: none
        org_header: false
        body:
          email: "{{TEST_EMAIL}}"
          password: "{{TEST_PASSWORD}}"
        assert:
          status: 200
          json_path:
            "$.access_token": { exists: true }
        capture:
          APP_JWT: "$.access_token"

tests/regression/01_api.yaml — exercise the API with the captured token:

meta:
  product: myapp
  layer: api
  runner: httpx
  endpoint: "http://localhost:8000"
  default_auth: prod

auth:
  prod:
    type: bearer
    token: "{{APP_JWT}}"

groups:
  - id: 1
    name: "Items"
    priority: high
    tests:
      - id: "A.1"
        name: "List items returns array"
        method: GET
        path: "/api/v1/items"
        assert:
          status: 200
          json_path:
            "$": { not_empty: true }

Run the tests:

regrun run tests/regression/

Expected output:

tests/regression/  •  2 tests

  [PASS]  S.1  Login and capture JWT         (142ms)
  [PASS]  A.1  List items returns array       (38ms)

  2 passed, 0 failed  •  180ms

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How It Works (Execution Model)

File ordering: The setup layer always runs first. All other files run alphabetically by filename. Numeric prefixes (00_, 01_, 02_) enforce the intended order.

Setup dependency: When you pass --layer api or --layer mcp, the setup file is auto-included and runs before the target layer. When setup runs as a dependency, --group and --priority filters are not applied to it — it always runs in full so captured variables stay available. Filters apply to setup only when it is the explicit target (--layer setup). Skip setup entirely with --skip-setup when variables are already populated from a prior run segment.

Variable persistence: File-level variables are merged once per file at parse time. A variable already set by an earlier file — for example RUN_ID defined in setup — is never overwritten by a later file's variables block. This ensures identifiers stay consistent across the entire run.

Layer concept: Tests are organised into four layers, processed in this order:

Layer	Purpose
setup	Auth, seed data, environment configuration
api	REST API surface tests
mcp	MCP tool tests
chat	WebSocket and streaming tests

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CLI Reference

regrun run TEST_DIR [OPTIONS]

TEST_DIR is a path to a directory containing YAML test files.

Flag	Type	Default	Description
--layer	setup|api|mcp|chat	all	Filter to one layer (setup auto-included)
--group	1,2,3	all	Comma-separated group IDs
--priority	high|medium|low	all	Filter groups by priority
--dry-run	flag	false	Print test plan without executing
--output	text|json	text	Output format
--verbose, -v	flag	false	Log full request/response bodies
--fail-fast	flag	false	Stop on first failure
--skip-setup	flag	false	Skip setup layer

Examples:

# Smoke test only
regrun run tests/regression/ --priority high

# MCP layer only
regrun run tests/regression/ --layer mcp

# Specific groups as JSON
regrun run tests/regression/ --group 1,3 --output json

# Preview without running
regrun run tests/regression/ --dry-run

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YAML Schema Reference

meta block (required)

meta:
  product: myapp              # Used for reporting only — does not need to match any registered name
  layer: api                  # setup | api | mcp | chat
  runner: httpx               # httpx | fastmcp | bash | websocket
  endpoint: "http://localhost:8000"      # Base URL for httpx runner
  mcp_endpoint: "http://localhost:9000"  # MCP base URL — falls back to endpoint if omitted
  default_auth: prod          # Auth key applied to all tests without explicit auth:
  env_file: ".env.test"       # Path to .env file, relative to the test file's directory

The product field appears in report output. It does not need to match any external registry.

variables block

variables:
  RUN_ID: "{{timestamp}}"               # Unix timestamp + 4 hex chars (unique per run)
  TODAY: "{{date}}"                     # YYYY-MM-DD
  REQUEST_ID: "{{uuid}}"               # UUID4
  API_TOKEN: "{{env.MY_SECRET_TOKEN}}"  # Environment variable passthrough
  BASE_EMAIL: "[e-mail]"          # Static value

Built-in variables:

Variable	Description
{{timestamp}}	Unix timestamp + 4 hex chars — unique per run, use as resource name suffix
{{date}}	Current date as YYYY-MM-DD
{{uuid}}	UUID4
{{env.VAR_NAME}}	Reads VAR_NAME from the process environment

Full Jinja2 template syntax is supported. The engine runs in StrictUndefined mode: an undefined variable logs a warning and returns the raw template string rather than raising an exception.

Variables set by earlier files are preserved. Downstream files skip re-initialization of keys that already exist in the store.

auth block

auth:
  prod:
    type: bearer                # bearer | api_key
    token: "{{APP_JWT}}"
    org_header: "myapp"         # Sets X-Org-Slug header — omit if not needed
  service_key:
    type: api_key
    token: "{{SERVICE_API_KEY}}"

groups block

groups:
  - id: 1
    name: "Auth Flow"
    priority: high          # high | medium | low  (default: medium)
    context: prod           # prod | fresh | both  (default: prod)
    tests:
      - ...
  - id: 2
    name: "CRUD Operations"
    priority: medium
    tests:
      - ...

Test fields by runner

httpx (REST API)

- id: "A.2"
  name: "Create item"
  method: POST
  path: "/api/v1/items"
  auth: prod                  # Named auth key, "none", or omit to use default_auth
  org_header: true            # false to suppress X-Org-Slug
  body:
    name: "Widget {{RUN_ID}}"
    price: 9.99
  query_params:
    expand: metadata
  assert:
    status: 201
    json_path:
      "$.id": { exists: true }
      "$.name": { starts_with: "Widget" }
  capture:
    ITEM_ID: "$.id"

fastmcp (MCP tools)

- id: "M.1"
  name: "List items via MCP"
  tool: items_list
  args:
    status: "active"
    limit: 10
  auth: service_key
  assert:
    is_error: false
    json_path:
      "$[0].id": { exists: true }
      "$": { not_empty: true }
  capture:
    FIRST_ITEM_ID: "$[0].id"

bash (shell commands)

- id: "S.2"
  name: "Seed test user"
  runner: bash
  commands:
    - cmd: |
        docker exec myapp-postgres psql -U postgres -d myapp \
          -c "INSERT INTO users (email) VALUES ('[e-mail]') ON CONFLICT DO NOTHING;"
      capture:
        RAW_OUTPUT: stdout
  assert:
    last_exit_code: 0
    contains: "INSERT"

Bash commands run from the directory where you invoke regrun, not from the test file location. Use absolute paths or docker exec rather than relative paths.

websocket (streaming)

- id: "C.1"
  name: "Chat session produces response"
  url: "ws://localhost:8000/api/v1/ws/chat?session_id={{SESSION_ID}}"
  send:
    message: "What is the status of my account?"
    session_id: "{{SESSION_ID}}"
  wait_for: "agent_completed"      # Event type that terminates collection
  timeout: 60000                   # Milliseconds (overrides file-level timeout)
  ws_config:
    text_event: text_delta         # Override only if your server uses non-default field names
  assert:
    has_error: false
    json_path:
      "$.response_text": { not_empty: true }
      "$.event_count": { gt: 1 }
  capture:
    CHAT_RESPONSE: "$.response_text"

The runner connects, sends send as a JSON frame, collects events until wait_for is received, and returns an aggregated result dict:

Field	Type	Description
response_text	str	All text_delta fragments joined
events	list[str]	Ordered list of all event types received
event_count	int	Total number of events
tool_calls	list[str]	Tool names from tool_call events
duration_ms	float	Wall time from connect to termination event
error	str|null	Error message if an error event was received or timeout occurred

ws_config options (all have defaults — omit unless overriding):

Field	Default	Description
event_type_field	event_type	Primary key used to read the event type from each frame
event_type_fallback	type	Fallback key if primary is absent
text_event	text_delta	Event type whose payload contributes to response_text
text_field	data.delta	Dot-path to the text content within a text event
tool_call_event	tool_call	Event type that signals a tool was called
tool_name_field	data.tool_name	Dot-path to the tool name within a tool call event
error_event	error	Event type that signals an error
error_field	data.content	Dot-path to the error message within an error event

Per-test runner override — used in setup files that mix bash and httpx:

# In a file with meta.runner: bash, a single test can use httpx instead:
- id: "P.1"
  runner: httpx               # Overrides the file-level meta.runner
  method: POST
  path: "/api/v1/auth/login"
  auth: none
  org_header: false
  body:
    email: "{{TEST_EMAIL}}"
    password: "{{TEST_PASSWORD}}"
  assert:
    status: 200
  capture:
    APP_JWT: "$.access_token"

Pure api or mcp files should not use per-test runner: overrides — the file's meta.runner applies uniformly.

---

Assertion Vocabulary

Top-level assertions

Key	Values	Runner
status	200 or [200, 201]	httpx
is_error	true|false	fastmcp
has_error	true|false	websocket
last_exit_code	0	bash
contains	substring string	all runners

json_path operators

Each entry under json_path: maps a JSONPath expression to one operator:

Operator	Example	Description
exists	"$.id": { exists: true }	Field presence check
equals	"$.status": { equals: "active" }	Exact match (string-coerced fallback)
contains	"$.name": { contains: "Widget" }	Substring
gt	"$.total": { gt: 0 }	Greater than
gte	"$.count": { gte: 1 }	Greater than or equal
lt	"$.errors": { lt: 10 }	Less than
lte	"$.errors": { lte: 5 }	Less than or equal
starts_with	"$.key": { starts_with: "ntk_" }	Prefix check
matches	"$.slug": { matches: "^[a-z0-9-]+$" }	Regex search
not_empty	"$.items": { not_empty: true }	Value is non-empty string, list, or dict
not_contains	"$.results[*].id": { not_contains: "{{FORBIDDEN_ID}}" }	Array exclusion — passes when no value matched by the path equals the expected value (all matches, string-coerced); empty/missing match set passes

Note: numeric operators (gt, gte, lt, lte) are the correct names. greater_than, less_than, >=, and <= are not valid.

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Variable Capture

capture:
  ITEM_ID: "$.id"                # JSONPath from JSON response
  OWNER_EMAIL: "$.owner.email"   # Nested path
  RAW_OUTPUT: stdout             # Full stdout (bash runner only)

Captured variables are stored in the shared VariableStore and are available to all subsequent tests in the run — including tests in later YAML files. This is how a JWT captured in 00_setup.yaml is accessible in 01_api_surface.yaml without any re-declaration.

Collision avoidance: suffix resource names with {{RUN_ID}} to prevent conflicts across runs:

body:
  name: "Test item {{RUN_ID}}"

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Auth Patterns Guide

Pattern	YAML	When to use
File default	meta.default_auth: prod	All tests in file use the same auth
Per-test override	auth: admin	One test needs different credentials
No auth	auth: none	Login, register, org creation endpoints
Suppress org header	org_header: false	Bare-domain endpoints where X-Org-Slug causes 400 errors

auth: none is a string literal, not YAML null. Always write auth: none explicitly — writing auth: with no value parses as null and fails.

Multi-file auth flow: setup acquires credentials, downstream files consume them.

00_setup.yaml:

meta:
  runner: httpx
  endpoint: "http://localhost:8000"
# No default_auth — login endpoint needs no auth

groups:
  - id: 1
    tests:
      - id: "S.1"
        name: "Login"
        method: POST
        path: "/api/v1/auth/login"
        auth: none
        org_header: false
        body:
          email: "{{TEST_EMAIL}}"
          password: "{{TEST_PASSWORD}}"
        assert:
          status: 200
        capture:
          APP_JWT: "$.access_token"

01_api_surface.yaml:

meta:
  runner: httpx
  endpoint: "http://localhost:8000"
  default_auth: prod          # APP_JWT now available from setup

auth:
  prod:
    type: bearer
    token: "{{APP_JWT}}"      # Captured in 00_setup.yaml
    org_header: "myapp"

---

Complete Example

A self-contained two-file example for a fictional myapp REST service.

tests/regression/00_setup.yaml

meta:
  product: myapp
  layer: setup
  runner: bash
  endpoint: "http://localhost:8000"

variables:
  RUN_ID: "{{timestamp}}"
  TEST_EMAIL: "regtest-{{RUN_ID}}@example.com"
  TEST_PASSWORD: "TestPass123!"

groups:
  - id: 1
    name: "Seed"
    priority: high
    tests:
      - id: "S.1"
        name: "Verify database is ready"
        runner: bash
        commands:
          - cmd: "docker exec myapp-postgres pg_isready -U postgres"
            capture:
              RAW_OUTPUT: stdout
        assert:
          last_exit_code: 0
          contains: "accepting connections"

      - id: "S.2"
        name: "Login and capture JWT"
        runner: httpx
        method: POST
        path: "/api/v1/auth/login"
        auth: none
        org_header: false
        body:
          email: "{{TEST_EMAIL}}"
          password: "{{TEST_PASSWORD}}"
        assert:
          status: 200
          json_path:
            "$.access_token": { exists: true }
        capture:
          APP_JWT: "$.access_token"

      - id: "S.3"
        name: "Create API key"
        runner: httpx
        method: POST
        path: "/api/v1/api-keys"
        auth: session
        body:
          name: "regression-key-{{RUN_ID}}"
        assert:
          status: 201
          json_path:
            "$.key": { starts_with: "ak_" }
        capture:
          API_KEY: "$.key"

auth:
  session:
    type: bearer
    token: "{{APP_JWT}}"

tests/regression/01_api_surface.yaml

meta:
  product: myapp
  layer: api
  runner: httpx
  endpoint: "http://localhost:8000"
  default_auth: prod

auth:
  prod:
    type: bearer
    token: "{{APP_JWT}}"
    org_header: "myapp"

groups:
  - id: 1
    name: "Items CRUD"
    priority: high
    tests:
      - id: "A.1"
        name: "List items"
        method: GET
        path: "/api/v1/items"
        assert:
          status: 200
          json_path:
            "$": { not_empty: true }

      - id: "A.2"
        name: "Create item"
        method: POST
        path: "/api/v1/items"
        body:
          name: "Regression item {{RUN_ID}}"
          price: 19.99
        assert:
          status: 201
          json_path:
            "$.id": { exists: true }
            "$.name": { contains: "Regression item" }
        capture:
          ITEM_ID: "$.id"

      - id: "A.3"
        name: "Get item by ID"
        method: GET
        path: "/api/v1/items/{{ITEM_ID}}"
        assert:
          status: 200
          json_path:
            "$.id": { equals: "{{ITEM_ID}}" }
            "$.price": { equals: "19.99" }

      - id: "A.4"
        name: "Delete item"
        method: DELETE
        path: "/api/v1/items/{{ITEM_ID}}"
        assert:
          status: 204

Run it:

regrun run tests/regression/

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Environment Variables

Variable	Default	Description
REGRUN_TIMEOUT	30	Per-test HTTP timeout (seconds)
REGRUN_MCP_TIMEOUT	60	Per-test MCP call timeout (seconds)
REGRUN_WS_TIMEOUT	30	Per-test WebSocket timeout (seconds)
REGRUN_VERBOSE	false	Log full request/response bodies
REGRUN_API_ENDPOINT	—	Override meta.endpoint globally (for CI)
REGRUN_MCP_ENDPOINT	—	Override meta.mcp_endpoint globally (for CI)

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CI Integration

In CI, services run as Docker containers with network aliases instead of *.localhost domains. Use the endpoint override variables to point regrun at the container aliases.

GitLab CI:

regression:
  stage: test
  services:
    - name: myapp-api:latest
      alias: api
    - name: myapp-mcp:latest
      alias: mcp
  variables:
    REGRUN_API_ENDPOINT: "http://api:8000"
    REGRUN_MCP_ENDPOINT: "http://mcp:9000"
  script:
    - pip install regrun
    - regrun run tests/regression/

GitHub Actions:

jobs:
  regression:
    runs-on: ubuntu-latest
    services:
      api:
        image: myapp-api:latest
        ports:
          - 8000:8000
    steps:
      - uses: actions/checkout@v4
      - run: pip install regrun
      - run: regrun run tests/regression/
        env:
          REGRUN_API_ENDPOINT: "http://localhost:8000"

The endpoint override applies to every test file in the run. YAML files keep their local *.localhost URLs for developer use; CI overrides them without any file changes.

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File Structure

Recommended test directory layout:

tests/regression/
  00_setup.yaml          # Setup: auth, seed data, environment checks
  01_api_surface.yaml    # REST API surface tests
  02_mcp_surface.yaml    # MCP tool tests
  03_chat_surface.yaml   # WebSocket / streaming tests

Numeric prefixes control alphabetical sort order. The setup layer is always processed first regardless of filename, but 00_ makes the intent explicit and keeps directory listings readable.

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Development

Install dependencies and run the test suite:

poetry install
poetry run pytest

Tests live at tests/integration/cli/ and cover CLI behaviour end-to-end.

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License

MIT