Principle:Langchain ai Langchain Compatibility Testing

Overview

Compatibility Testing is the practice of verifying that a new version of a foundational library remains backward-compatible with already-published packages that depend on it.

Description

In a monorepo with layered packages, a core library sits at the bottom of the dependency graph. Changes to core can silently break partner integrations and downstream consumers even if core's own tests pass. Compatibility testing addresses this by:

1. Identifying the latest published versions of key dependent packages.
2. Checking out the source code for those packages at their published state (using Git tags).
3. Installing the new, unreleased core alongside the old, published partner code.
4. Running the partner's test suite to detect regressions.

This pattern is especially important when:

• The core library changes internal interfaces, abstract base classes, or serialization formats.
• Type signatures or method behaviors are modified in ways not covered by the core's own test suite.
• A partner package relies on undocumented behavior of the core library.

The testing uses a matrix strategy so that multiple partner packages can be tested in parallel, and fail-fast: false ensures that a failure in one partner does not prevent testing the others.

Usage

Use compatibility testing when:

• Releasing a new version of a core/foundational library.
• Evaluating whether a proposed API change would break published consumers.
• Adding a new partner package to the compatibility matrix.

Practical Guide

1. Build the new core library wheel.
2. For each partner package in the compatibility matrix:
   a. Find the latest published tag for that partner.
   b. Checkout the partner source at that tag.
   c. Install the partner's dependencies normally.
   d. Override the core dependency with the new wheel.
   e. Run the partner's integration test suite.
3. If any partner's tests fail, block the core release.

Pseudocode:

core_wheel = build("libs/core")

for partner in ["anthropic", "openai", ...]:
    latest_tag = find_latest_tag("langchain-" + partner)
    checkout(tag=latest_tag, paths=["libs/partners/" + partner, "libs/standard-tests/"])

    cd("libs/partners/" + partner)
    install_deps(groups=["test", "test_integration"])
    install(core_wheel)  # override published core with new wheel

    run("make integration_tests")

Related Pages

• Implementation:Langchain_ai_Langchain_Core_Compatibility_Tests