Code Coverage for Golang Applications

Code coverage for a Golang sample app

To generate code coverage for Golang applications using the RKTracer tool, you need to add the RKTracer runtime library to the Go installation folder, be it a Windows or a Linux platform, and instrument the application with the RKTracer tool. Then test the instrumented application and generate code coverage.

Adding the RKTracer runtime library to the Go installation

Add the RKTracer runtime library rkgo to the GOROOT, i.e., the Go installation folder. It is a one-time setup.

Windows or Linux. To integrate the RKTracer runtime library source file into the Go installation, follow the instructions below.

Step 1. Open a command prompt and run the command.

go env GOROOT

If Go is on the path, then you should see the following output. In my case, it is in the path /usr/lib/go-1.26.

/usr/lib/go-1.26

Step 2. The command output gives us the path where Go is installed. Now create an rkgo folder in the src folder of the Go installation and copy rkgo.go from the RKTracer installation folder into the rkgo folder.

sudo cp  $HOME/rktracer/share/rktracer/rkgo.go /usr/lib/go-x.x/src/rkgo/

Replace go-x.x with your actual Go version folder from the go env GOROOT output (for example, go-1.26).

Code coverage for Golang applications example

Identify the project folder that needs to be instrumented and generate coverage data. Please make sure the project is configured and you are able to test it.

Enable the RKTracer tool

Then execute the following command to Turn ON (instrument) or Turn OFF (un-instrument) the RKTracer tool. RKTracer will instrument all Go source files in a folder recursively.

rktracer -on  path-toproject/module/ go  -v
rktracer -off  path-toproject/module/ go  -v

• go at the end means RKTracer needs to instrument only Go source files.
• -v at the end means RKTracer will show a verbose instrumentation log.

The above command will instrument all the Go source files in the project folder recursively. Rebuild the application with the go clean and go build commands.

go clean
go build

Run tests on the instrumented application

Testing can be unit testing, or functional or integration testing of the application.

Once the testing is completed, you should see the file rk-coverage.txt. Now copy this file to the project folder, or the path where you executed the command rktracer -on path-to-project/module/ go -v to instrument the project folder using the RKTracer tool.

You should also see the rktracer folder with the RKTracer tool intermediate files. The rktracer folder is generated at the time of instrumentation. You need to copy the rk-coverage.txt file parallel to the rktracer folder in the project.

Generate code coverage reports

Once you have the rk-coverage.txt file, run the rkresults command to generate the HTML reports. Ensure that you run the rkresults command in the application root folder, or where you have the rktracer folder generated at the time of build/instrumentation.

rkresults

The rkresults command will search for the coverage data file rk-coverage.txt and map it with the JSON files (generated during instrumentation) in the rktracer folder, then generate the HTML reports. You can manually open the HTML report using index.html.

rktracer -off  path-toproject/module/ go  -v

Code coverage for Golang setup in Docker

You can generate code coverage for Golang applications inside Docker or any CI container. Install RKTracer into the image, activate the trial licence, then copy the rkgo runtime into both the Go installation (GOROOT) and your module's vendor tree. Finally, instrument the sources with rktracer -on before you build and test. The setup commands below correspond to the container build script:

# fail fast and echo each command
set -ex

# install RKTracer into the image and put it on PATH
sh rktracer-installer-linux.run --accept-license --quiet --target /opt/rktracer
export PATH="/opt/rktracer/bin:$PATH"
which rktracer

# activate the trial licence and verify
cp trial-license.lic /opt/rktracer
rktracer -version

# add the rkgo runtime to GOROOT and to the module vendor tree
mkdir /usr/local/go/rkgo
cp /opt/rktracer/share/rktracer/rkgo.go /usr/local/go/rkgo/
mkdir -p /app/vendor/rkgo
cp /opt/rktracer/share/rktracer/rkgo.go /app/vendor/rkgo/

# instrument the Go sources under ./src
rktracer -on src go -v

set +ex

Dropped into a Dockerfile, the same steps look like this. After the image is built, run go build, execute your tests, and run rkresults to produce the HTML coverage report exactly as on the command line.

FROM golang:1.21

WORKDIR /app
COPY . .

# RKTracer installer + trial licence are copied in alongside the sources
RUN set -ex \
 && sh rktracer-installer-linux.run --accept-license --quiet --target /opt/rktracer \
 && export PATH="/opt/rktracer/bin:$PATH" \
 && cp trial-license.lic /opt/rktracer \
 && rktracer -version \
 && mkdir -p /usr/local/go/rkgo /app/vendor/rkgo \
 && cp /opt/rktracer/share/rktracer/rkgo.go /usr/local/go/rkgo/ \
 && cp /opt/rktracer/share/rktracer/rkgo.go /app/vendor/rkgo/ \
 && rktracer -on src go -v \
 && go build ./...

ENV PATH="/opt/rktracer/bin:$PATH"

Enable coverage for selected files

Suppose you need code coverage for source files from three different folders, i.e., core, keys, power, and want to ignore coverage for the folders firmware_loader and lockdown. Edit rktracer.config in the RKTracer installation folder, go to the end of the file, and add the following information.

ignore *.go
instrument */power/* */core/* */keys/*
never */firmware_loader/* */lockdown/*

• ignore *.go ignores all Go source files from instrumentation.
• instrument instruments source files from the given folders.
• never ignores the selected folders.

Suppose you need code coverage for selected functions from three different files. Edit rktracer.config in the RKTracer installation folder, go to the end of the file, and set the following variables as shown below.

ignore *.go
instrument *file-X.go *file-Y.go *file-Z.go
function-ignore *
function-instrument fun_X() fun_Y() fun_Z()

• ignore *.go ignores all Go programming source files.
• instrument *file-X.go *file-Y.go *file-Z.go instruments only these three source files.
• function-ignore * then ignores all functions in the above three files.
• function-instrument fun_X() fun_Y() fun_Z() does not ignore these three functions from these three files during instrumentation.

Golang code coverage FAQ

Related code coverage guides

Working across more than one language or toolchain? These guides use the same RKTracer instrument, test, and rkresults workflow:

• Code coverage for Python
• Code coverage for C and C++ with CMake
• Code coverage for Java with Maven
• Code coverage for C# and .NET
• Code coverage for JavaScript and TypeScript
• RKTracer code coverage tool overview