How can I measure test coverage in Go?

How to Measure Test Coverage in Go

One of the challenges in software testing is determining the extent to which tests cover the code under test. This metric, known as test coverage, is essential for ensuring that tests are comprehensive and effective.

Go's Test Coverage Capabilities

In Go versions 1.2 and later, the go test command now supports the calculation and display of test coverage results. To enable coverage, simply use the -cover flag when running tests.

go test -cover

This will generate a basic coverage report, indicating the percentage of statements covered by the tests.

Detailed Coverage Analysis

For more detailed coverage reports, use the -coverprofile flag to specify an output file that will contain the coverage profile. This profile can then be analyzed using the go tool cover command.

go test -coverprofile=coverage.out
go tool cover -html=coverage.out

The -html flag generates an HTML report that provides a visual representation of the coverage, highlighting lines that are not covered.

Blackbox Testing

To measure coverage for blackbox tests (tests that do not have access to the internal state of the package), use the -coverpkg flag. This flag specifies the package that should be instrumented for coverage.

go test -coverprofile=.coverage.html -coverpkg=your/pkg your/pkg/pkg_test

Recent Enhancements

In Go 1.20, integration tests can now be included in the coverage analysis. The go build -cover command can be used to build coverage-instrumented binaries. These binaries can then be used in integration tests to extend the scope of coverage testing.

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