golang

GO Testing Cheatsheet

Unit Tests

Action	Command	Notes
Run tests in directory	go test .
Run tests in directory tree	go test ./...
Run tests matching regex	go test ./... --run=NameOfTest
Run tests in specific file	go test ./file_test.go ./file.go	Include the file the test depends on for compilation.
Clean test cache	go clean --testcache

Code Coverage

Remember: the only absolute conclusion that can be made is that code with zero coverage isn't unit tested at all. Code coverage does not guarantee the unit tests themselves are accurate and/or comprehensive.

Action	Command	Notes
See basic summary	go test ./... --cover
Save report to text file	go test ./... --coverprofile=coverage.out	It's community convention to use the .out file extension for test results.
See summary of a saved report	go tool cover --func=coverage.out
See details of a saved report	go tool cover --html=coverage.out

Generate and View Code Coverage Heatmap

1. Generate and save coverage report with frequency information: go test ./... --covermode=count --coverprofile=coverage.out.
2. See details of the saved report: go tool cover --html=coverage.out.

Benchmark Tests

Beware high P-Values (wikipedia); benchmark results with a p-value greater than 0.05 are probably useless.

Action	Command	Notes
Run benchmarks in directory	go test . --bench=.	Also runs unit tests in directory.
Run benchmarks in directory tree	go test ./... --bench=.	Also runs unit tests in directory tree.
Run only benchmarks in directory tree	go test ./... --run=^$ --bench=.	Works by using a regex that matches nothing.
Run benchmarks matching regex	go test ./... --bench=NameOfTest
Run benchmarks matching regex for 20 seconds	go test ./... --bench=NameOfTest --benchtime=20s	Increasing the test duration is usually the best way to reduce p-values for long-running functions.
Run benchmarks matching regex 10 times	go test ./... --bench=NameOfTest --count=10	Increasing iterations is usually the best way to reduce p-values for short-running functions.

Comparing Benchmarks

1. Install Russ Cox's benchstat utility: go get golang.org/x/perf/cmd/benchstat.
2. Run the benchmark saving the results to a text file: go test ./... --bench=NameOfTest --count=10 > original.txt.
3. Make your changes to the function under benchmark testing.
4. Re-run the same benchmark saving the results to a different text file: go test ./... --bench=NameOfTest --count=10 > refactor.txt.
5. Compare using the benchstat util: benchstat original.txt refactor.txt.

Additional Reading

• Why bother writing tests at all? (mirror)

Unit Testing

• Golang basics - writing unit tests (mirror)
• Prefer table driven tests (mirror)
• Testable Examples in Go (mirror)
• A pattern for Go tests (mirror)
• Unit testing HTTP servers

Code Coverage

• The Pitfalls of Code Coverage (mirror)

Benchmark Testing

• Analyzing the performance of Go functions with benchmarks (mirror)