Regression testing for chains in LangChain - Step-by-Step Execution

Concept Flow - Regression testing for chains

Write initial chain code

↓

Create test cases with expected outputs

↓

Run chain with test inputs

↓

Compare actual output to expected

↓

Pass test

↓

Save tests

↓

Repeat tests after changes

Shows the flow of writing chain code, creating tests, running them, checking results, fixing code if needed, and repeating tests to catch regressions.

Execution Sample

LangChain

from langchain.chains import SimpleChain

def test_chain():
    chain = SimpleChain()
    output = chain.run("Hello")
    assert output == "Hello World"

A simple test runs a chain with input 'Hello' and checks if output matches expected 'Hello World'.

Execution Table

Step	Action	Input	Expected Output	Actual Output	Test Result
1	Run chain with input	"Hello"	"Hello World"	"Hello World"	Pass
2	Run chain with input	"Test"	"Test World"	"Test World"	Pass
3	Run chain with input	"Fail"	"Fail World"	"Fail Wrld"	Fail
4	Fix chain code	N/A	N/A	N/A	N/A
5	Re-run chain with input	"Fail"	"Fail World"	"Fail World"	Pass

💡 All tests pass after fixing chain code; regression testing confirms no output breaks.

Variable Tracker

Variable	Start	After Step 1	After Step 2	After Step 3	After Step 4	After Step 5
output	None	"Hello World"	"Test World"	"Fail Wrld"	None (fixed)	"Fail World"
test_result	None	Pass	Pass	Fail	N/A	Pass

Key Moments - 2 Insights

Why does the test fail at step 3 even though the input looks similar?

At step 3, the actual output "Fail Wrld" is missing the 'o' compared to expected "Fail World". This shows a bug in the chain code that regression testing catches.

Why do we re-run tests after fixing the chain code?

Re-running tests (step 5) confirms the fix works and no new bugs were introduced, ensuring the chain behaves as expected.

Visual Quiz - 3 Questions

Look at the execution table, what is the test result at step 3?

A Pass

B Fail

C Skipped

D Error

💡 Hint

Check the 'Test Result' column at step 3 in the execution_table.

At which step is the chain code fixed?

A Step 2

B Step 3

C Step 4

D Step 5

💡 Hint

Look for the action 'Fix chain code' in the execution_table.

If the output at step 5 was still "Fail Wrld", what would the test result be?

A Pass

B Fail

C Error

D Skipped

💡 Hint

Compare expected and actual output in the execution_table at step 3 and 5.

Concept Snapshot

Regression testing for chains:
- Write chain code
- Create tests with inputs and expected outputs
- Run chain and compare outputs
- Fix bugs if outputs differ
- Re-run tests to confirm fixes
- Ensures chain changes don't break expected behavior

Full Transcript

Regression testing for chains means writing tests that run your chain with known inputs and check if the outputs match what you expect. If outputs differ, you fix the chain code and run tests again. This process helps catch bugs early and ensures your chain keeps working correctly after changes. The flow starts with writing chain code, creating test cases, running tests, checking results, fixing code if needed, and repeating tests. The example shows a chain tested with inputs like 'Hello' and 'Fail'. The test fails when output misses a letter, so the code is fixed and tests pass again. This cycle helps keep your chain reliable.