Overview

Golden Data test framework provides ability to run and manage tests that produce an output which is verified by comparing it to the checked-in, known valid output. Any differences result in test failure and either the code or expected output has to be updated.

Golden Data tests excel at bulk diffing of failed test outputs and bulk accepting of new test outputs.

When to use Golden Data tests?

Code under test produces a deterministic output: That way tests can consistently succeed or fail.
Incremental changes to code under test or test fixture result in incremental changes to the output.
As an alternative to ASSERT for large output comparison: Serves the same purpose, but provides tools for diffing/updating.
The outputs can't be objectively verified (e.g. by verifying well known properties). Examples:
- Verifying if sorting works, can be done by verifying that output is sorted. SHOULD NOT use Golden Data tests.
- Verifying that pretty printing works, MAY use Golden Data tests to verify the output, as there might not be well known properties or those properties can easily change.
As stability/versioning/regression testing. Golden Data tests by storing recorded outputs, are good candidate for preserving behavior of legacy versions or detecting undesired changes in behavior, even in cases when new behavior meets other correctness criteria.

Best practices for working with Golden Data tests

Tests MUST produce text output that is diffable can be inspected in the pull request.
Tests MUST produce an output that is deterministic and repeatable. Including running on different platforms. Same as with ASSERT_EQ.
Tests SHOULD produce an output that changes incrementally in response to the incremental test or code changes.
Multiple test variations MAY be bundled into a single test. Recommended when testing same feature with different inputs. This helps reviewing the outputs by grouping similar tests together, and also reduces the number of output files.
Changes to test fixture or test code that affect non-trivial amount test outputs MUST BE done in separate pull request from production code changes:
- Pull request for test code only changes can be easily reviewed, even if large number of test outputs are modified. While such changes can still introduce merge conflicts, they don't introduce risk of regression (if outputs were valid
- Pull requests with mixed production
Tests in the same suite SHOULD share the fixtures when appropriate. This reduces cost of adding new tests to the suite. Changes to the fixture may only affect expected outputs from that fixtures, and those output can be updated in bulk.
Tests in different suites SHOULD NOT reuse/share fixtures. Changes to the fixture can affect large number of expected outputs. There are exceptions to that rule, and tests in different suites MAY reuse/share fixtures if:
- Test fixture is considered stable and changes rarely.
- Tests suites are related, either by sharing tests, or testing similar components.
- Setup/teardown costs are excessive, and sharing the same instance of a fixture for performance reasons can't be avoided.
Tests SHOULD print both inputs and outputs of the tested code. This makes it easy for reviewers to verify of the expected outputs are indeed correct by having both input and output next to each other. Otherwise finding the input used to produce the new output may not be practical, and might not even be included in the diff.
When resolving merge conflicts on the expected output files, one of the approaches below SHOULD be used:
- "Accept theirs", rerun the tests and verify new outputs. This doesn't require knowledge of production/test code changes in "theirs" branch, but requires re-review and re-acceptance of c hanges done by local branch.
- "Accept yours", rerun the tests and verify the new outputs. This approach requires knowledge of production/test code changes in "theirs" branch. However, if such changes resulted in straightforward and repetitive output changes, like due to printing code change or fixture change, it may be easier to verify than reinspecting local changes.
Expected test outputs SHOULD be reused across tightly-coupled test suites. The suites are tightly-coupled if:
- Share the same tests, inputs and fixtures.
- Test similar scenarios.
- Test different code paths, but changes to one of the code path is expected to be accompanied by changes to the other code paths as well.
Tests SHOULD use different test files, for legitimate and expected output differences between those suites.

Examples:
- Functional tests, integration tests and unit tests that test the same behavior in different environments.
- Versioned tests, where expected behavior is the same for majority of test inputs/scenarios.
AVOID manually modifying expected output files. Those files are considered to be auto generated. Instead, run the tests and then copy the generated output as a new expected output file. See "How to diff and accept new test outputs" section for instructions.

How to use write Golden Data tests?

Each golden data test should produce a text output that will be later verified. The output format must be text, but otherwise test author can choose a most appropriate output format (text, json, bson, yaml or mixed). If a test consists of multiple variations each variation should be clearly separated from each other.

Note: Test output is usually only written. It is ok to focus on just writing serialization/printing code without a need to provide deserialization/parsing code.

When actual test output is different from expected output, test framework will fail the test, log both outputs and also create following files, that can be inspected later:

<output_path>/actual/<test_path> - with actual test output
<output_path>/expected/<test_path> - with expected test output

CPP tests

::mongo::unittest::GoldenTestConfig - Provides a way to configure test suite(s). Defines where the expected output files are located in the source repo.

::mongo::unittest::GoldenTestContext - Provides an output stream where tests should write their outputs. Verifies the output with the expected output that is in the source repo

See: golden_test.h

Example:

#include "mongo/unittest/golden_test.h"

GoldenTestConfig myConfig("src/mongo/my_expected_output");
TEST(MySuite, MyTest) {
    GoldenTestContext ctx(myConfig);
    ctx.outStream() << "print something here" << std::endl;
    ctx.outStream() << "print something else" << std::endl;
}

void runVariation(GoldenTestContext& ctx, const std::string& variationName, T input) {
    ctx.outStream() << "VARIATION " << variationName << std::endl;
    ctx.outStream() << "input: " << input << std::endl;
    ctx.outStream() << "output: " << runCodeUnderTest(input) << std::endl;
    ctx.outStream() << std::endl;
}

TEST_F(MySuiteFixture, MyFeatureATest) {
    GoldenTestContext ctx(myConfig);
    runMyVariation(ctx, "variation 1", "some input testing A #1")
    runMyVariation(ctx, "variation 2", "some input testing A #2")
    runMyVariation(ctx, "variation 3", "some input testing A #3")
}

TEST_F(MySuiteFixture, MyFeatureBTest) {
    GoldenTestContext ctx(myConfig);
    runMyVariation(ctx, "variation 1", "some input testing B #1")
    runMyVariation(ctx, "variation 2", "some input testing B #2")
    runMyVariation(ctx, "variation 3", "some input testing B #3")
    runMyVariation(ctx, "variation 4", "some input testing B #4")
}

Also see self-test: golden_test_test.cpp

How to diff and accept new test outputs on a workstation

Use buildscripts/golden_test.py command line tool to manage the test outputs. This includes:

diffing all output differences of all tests in a given test run output.
accepting all output differences of all tests in a given test run output.

Setup

buildscripts/golden_test.py requires a one-time workstation setup.

Note: this setup is only required to use buildscripts/golden_test.py itself. It is NOT required to just run the Golden Data tests when not using buildscripts/golden_test.py.

Create a yaml config file, as described by Appendix - Config file reference.
Set GOLDEN_TEST_CONFIG_PATH environment variable to config file location, so that is available when running tests and when running buildscripts/golden_test.py tool.

Automatic Setup

Use buildscripts/golden_test.py builtin setup to initialize default config for your current platform.

Instructions for Linux

Run buildscripts/golden_test.py setup utility

buildscripts/golden_test.py setup

Instructions for Windows

Run buildscripts/golden_test.py setup utility. You may be asked for a password, when not running in "Run as administrator" shell.

c:\python\python310\python.exe buildscripts/golden_test.py setup

Manual Setup (Default config)

This is the same config as that would be setup by the Automatic Setup

This config uses a unique subfolder folder for each test run. (default)

Allows diffing each test run separately.
Works with multiple source repos.

Instructions for Linux/macOS:

This config uses a unique subfolder folder for each test run. (default)

Allows diffing each test run separately.
Works with multiple source repos.

Create ~/.golden_test_config.yml with following contents:

outputRootPattern: /var/tmp/test_output/out-%%%%-%%%%-%%%%-%%%%
diffCmd: git diff --no-index "{{expected}}" "{{actual}}"

Update .bashrc, .zshrc

export GOLDEN_TEST_CONFIG_PATH=~/.golden_test_config.yml

alternatively modify /etc/environment or other configuration if needed by Debugger/IDE etc.

Instructions for Windows:

Create %LocalAppData%.golden_test_config.yml with the following contents:

outputRootPattern: 'C:\Users\Administrator\AppData\Local\Temp\test_output\out-%%%%-%%%%-%%%%-%%%%'
diffCmd: 'git diff --no-index "{{expected}}" "{{actual}}"'

Add GOLDEN_TEST_CONFIG_PATH=~/.golden_test_config.yml environment variable:

runas /profile /user:administrator "setx GOLDEN_TEST_CONFIG_PATH %LocalAppData%\.golden_test_config.yml"

Usage

List all available test outputs

$> buildscripts/golden_test.py list

Diff test results from most recent test run:

$> buildscripts/golden_test.py diff

This will run the diffCmd that was specified in the config file

Diff test results from most recent test run:

$> buildscripts/golden_test.py accept

This will copy all actual test outputs from that test run to the source repo and new expected outputs.

Get paths from most recent test run (to be used by custom tools)

Get expected and actual output paths for most recent test run:

$> buildscripts/golden_test.py get

Get expected and actual output paths for most most recent test run:

$> buildscripts/golden_test.py get_root

Get all available commands and options:

$> buildscripts/golden_test.py --help

How to diff test results from a non-workstation test run

Bulk folder diff the results:

Parse the test log to find the root output locations where expected and actual output files were written.
Then compare the folders to see the differences for tests that failed.

Example: (linux/macOS)

# Show the test run expected and actual folders:
$> cat test.log | grep "^{" | jq -s -c -r '.[] | select(.id == 6273501 ) | .attr.expectedOutputRoot + " " +.attr.actualOutputRoot ' | sort | uniq
# Run the recursive diff
$> diff -ruN --unidirectional-new-file --color=always <expected_root> <actual_root>

Find the outputs of tests that failed.

Parse logs and find the the expected and actual outputs for each failed test.

Example: (linux/macOS)

# Find all expected and actual outputs of tests that have failed
$> cat test.log | grep "^{" | jq -s '.[] | select(.id == 6273501 ) | .attr.testPath,.attr.expectedOutput,.attr.actualOutput'

Appendix - Config file reference

Golden Data test config file is a YAML file specified as:

outputRootPattern:
  type: String
  optional: true
  description:
    Root path patten that will be used to write expected and actual test outputs for all tests
    in the test run.
    If not specified a temporary folder location will be used.
    Path pattern string may use '%' characters in the last part of the path. '%' characters in
    the last part of the path will be replaced with random lowercase hexadecimal digits.
  examples: /var/tmp/test_output/out-%%%%-%%%%-%%%%-%%%%
    /var/tmp/test_output

diffCmd:
  type: String
  optional: true
  description: Shell command to diff a single golden test run output.
    {{expected}} and {{actual}} variables should be used and will be replaced  with expected and
    actual output folder paths respectively.
    This property is not used to decide whether the test passes or fails; it is only used to
    display differences once we've decided that a test failed.
  examples: git diff --no-index "{{expected}}" "{{actual}}"
    diff -ruN --unidirectional-new-file --color=always "{{expected}}" "{{actual}}"

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golden_data_test_framework.md

golden_data_test_framework.md

Overview

When to use Golden Data tests?

Best practices for working with Golden Data tests

How to use write Golden Data tests?

CPP tests

How to diff and accept new test outputs on a workstation

Setup

Automatic Setup

Manual Setup (Default config)

Usage

List all available test outputs

Diff test results from most recent test run:

Diff test results from most recent test run:

Get paths from most recent test run (to be used by custom tools)

How to diff test results from a non-workstation test run

Bulk folder diff the results:

Find the outputs of tests that failed.

Appendix - Config file reference

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golden_data_test_framework.md

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golden_data_test_framework.md

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Overview

When to use Golden Data tests?

Best practices for working with Golden Data tests

How to use write Golden Data tests?

CPP tests

How to diff and accept new test outputs on a workstation

Setup

Automatic Setup

Manual Setup (Default config)

Usage

List all available test outputs

Diff test results from most recent test run:

Diff test results from most recent test run:

Get paths from most recent test run (to be used by custom tools)

How to diff test results from a non-workstation test run

Bulk folder diff the results:

Find the outputs of tests that failed.

Appendix - Config file reference