Profiling test coverage
A great feature of the go test tool is the metrics and visualizations that it provides for test coverage.
Go ahead and try running the tests in our project using the -cover flag like so:
$ go test -cover ./...
? snippetbox.alexedwards.net/ui [no test files]
ok snippetbox.alexedwards.net/cmd/web 0.013s coverage: 45.7% of statements
snippetbox.alexedwards.net/internal/models/mocks coverage: 0.0% of statements
snippetbox.alexedwards.net/internal/validator coverage: 0.0% of statements
snippetbox.alexedwards.net/internal/assert coverage: 0.0% of statements
ok snippetbox.alexedwards.net/internal/models 0.128s coverage: 11.3% of statements
From the results here we can see that 46.9% of the statements in our cmd/web package are executed during our tests, and for our internal/models package the figure is 11.3%.
We can get a more detailed breakdown of test coverage by method and function by using the -coverprofile flag like so:
$ go test -coverprofile=/tmp/profile.out ./...
This will execute your tests as normal and — if all your tests pass — it will then write a coverage profile to a specific location. In the example above, we’ve instructed it to write the profile to /tmp/profile.out.
You can then view the coverage profile by using the go tool cover command like so:
$ go tool cover -func=/tmp/profile.out snippetbox.alexedwards.net/cmd/web/handlers.go:15: home 0.0% snippetbox.alexedwards.net/cmd/web/handlers.go:31: snippetView 92.9% snippetbox.alexedwards.net/cmd/web/handlers.go:62: snippetCreate 0.0% snippetbox.alexedwards.net/cmd/web/handlers.go:88: snippetCreatePost 0.0% snippetbox.alexedwards.net/cmd/web/handlers.go:131: userSignup 100.0% snippetbox.alexedwards.net/cmd/web/handlers.go:137: userSignupPost 88.5% snippetbox.alexedwards.net/cmd/web/handlers.go:192: userLogin 0.0% snippetbox.alexedwards.net/cmd/web/handlers.go:198: userLoginPost 0.0% snippetbox.alexedwards.net/cmd/web/handlers.go:256: userLogoutPost 0.0% snippetbox.alexedwards.net/cmd/web/handlers.go:277: ping 100.0% snippetbox.alexedwards.net/cmd/web/helpers.go:17: serverError 0.0% snippetbox.alexedwards.net/cmd/web/helpers.go:30: clientError 100.0% snippetbox.alexedwards.net/cmd/web/helpers.go:37: notFound 100.0% snippetbox.alexedwards.net/cmd/web/helpers.go:41: render 58.3% snippetbox.alexedwards.net/cmd/web/helpers.go:62: newTemplateData 100.0% snippetbox.alexedwards.net/cmd/web/helpers.go:73: decodePostForm 50.0% snippetbox.alexedwards.net/cmd/web/helpers.go:102: isAuthenticated 75.0% snippetbox.alexedwards.net/cmd/web/main.go:35: main 0.0% snippetbox.alexedwards.net/cmd/web/main.go:100: openDB 0.0% snippetbox.alexedwards.net/cmd/web/middleware.go:11: commonHeaders 100.0% snippetbox.alexedwards.net/cmd/web/middleware.go:26: logRequest 100.0% snippetbox.alexedwards.net/cmd/web/middleware.go:41: recoverPanic 66.7% snippetbox.alexedwards.net/cmd/web/middleware.go:61: requireAuthentication 16.7% snippetbox.alexedwards.net/cmd/web/middleware.go:83: noSurf 100.0% snippetbox.alexedwards.net/cmd/web/middleware.go:94: authenticate 38.5% snippetbox.alexedwards.net/cmd/web/routes.go:12: routes 100.0% snippetbox.alexedwards.net/cmd/web/templates.go:23: humanDate 100.0% snippetbox.alexedwards.net/cmd/web/templates.go:40: newTemplateCache 83.3% snippetbox.alexedwards.net/internal/models/snippets.go:31: Insert 0.0% snippetbox.alexedwards.net/internal/models/snippets.go:60: Get 0.0% snippetbox.alexedwards.net/internal/models/snippets.go:97: Latest 0.0% snippetbox.alexedwards.net/internal/models/users.go:34: Insert 0.0% snippetbox.alexedwards.net/internal/models/users.go:66: Authenticate 0.0% snippetbox.alexedwards.net/internal/models/users.go:98: Exists 100.0% total: (statements) 38.1%
An alternative and more visual way to view the coverage profile is to use the -html flag instead of -func.
$ go tool cover -html=/tmp/profile.out
This will open a browser window containing a navigable and highlighted representation of your code, similar to this:
The statements which get executed during your tests are colored green, and those that are not executed are colored red. This makes it easy to see exactly what code is currently covered by your tests (unless you have red-green color blindness).
You can take this a step further and use the -covermode=count option when running go test like so:
$ go test -covermode=count -coverprofile=/tmp/profile.out ./... $ go tool cover -html=/tmp/profile.out
Instead of just highlighting the statements in green and red, using -covermode=count makes the coverage profile record the exact number of times that each statement is executed during the tests.
When viewed in the browser, statements which are executed more frequently are then shown in a more saturated shade of green, similar to this:
