wasmbrowsertest

Run Go wasm tests easily in your browser.

If you have a codebase targeting the wasm platform, chances are you would want to test your code in a browser. Currently, that process is a bit cumbersome:

• The test needs to be compiled to a wasm file.
• Then loaded into an HTML file along with the wasm_exec.js.
• And finally, this needs to be served with a static file server and then loaded in the browser.

This tool automates all of that. So you just have to type GOOS=js GOARCH=wasm go test, and it automatically executes the tests inside a browser !

Quickstart

• go install github.com/agnivade/wasmbrowsertest@latest. This will place the binary in $GOPATH/bin, or $GOBIN, if that has a different value.
• Rename the binary to go_js_wasm_exec.
• Add $GOBIN to $PATH if it is not already done.
• Run tests as usual: GOOS=js GOARCH=wasm go test.
• You can also take a cpu profile. Set the -cpuprofile flag for that.

Ok, but how does the magic work ?

go test allows invocation of a different binary to run a test. go help test has a line:

-exec xprog
	    Run the test binary using xprog. The behavior is the same as
	    in 'go run'. See 'go help run' for details.

And go help run says:

By default, 'go run' runs the compiled binary directly: 'a.out arguments...'.
If the -exec flag is given, 'go run' invokes the binary using xprog:
	'xprog a.out arguments...'.
If the -exec flag is not given, GOOS or GOARCH is different from the system
default, and a program named go_$GOOS_$GOARCH_exec can be found
on the current search path, 'go run' invokes the binary using that program,
for example 'go_nacl_386_exec a.out arguments...'. This allows execution of
cross-compiled programs when a simulator or other execution method is
available.

So essentially, there are 2 ways:

• Either have a binary with the name of go_js_wasm_exec in your $PATH.
• Or set the -exec flag in your tests.

Use whatever works for you.

How is a CPU profile taken ?

A CPU profile is run during the duration of the test, and then converted to the pprof format so that it can be natively analyzed with the Go toolchain.

Can I run something which is not a test ?

Yep. GOOS=js GOARCH=wasm go run main.go also works. If you want to actually see the application running in the browser, set the WASM_HEADLESS variable to off like so WASM_HEADLESS=off GOOS=js GOARCH=wasm go run main.go.

Can I use this inside Travis ?

Sure.

Add these lines to your .travis.yml

addons:
  chrome: stable

install:
- go install github.com/agnivade/wasmbrowsertest@latest
- mv $GOPATH/bin/wasmbrowsertest $GOPATH/bin/go_js_wasm_exec
- export PATH=$GOPATH/bin:$PATH

Now, just setting GOOS=js GOARCH=wasm will run your tests using wasmbrowsertest. For other CI environments, you have to do something similar.

Can I use this inside Github Action?

Sure.

Add these lines to your .github/workflows/ci.yml

PS: adjust the go version you need in go-version section

on: [push, pull_request]
name: Unit Test
jobs:
  test:
    strategy:
      matrix:
        go-version: [1.xx.x]
        os: [ubuntu-latest]
    runs-on: ${{ matrix.os }}
    steps:
    - name: Install Go
      uses: actions/setup-go@v2
      with:
        go-version: ${{ matrix.go-version }}
    - name: Install chrome
      uses: browser-actions/setup-chrome@latest
    - name: Install dep
      run: go install github.com/agnivade/wasmbrowsertest@latest
    - name: Setup wasmexec
      run: mv $(go env GOPATH)/bin/wasmbrowsertest $(go env GOPATH)/bin/go_js_wasm_exec
    - name: Checkout code
      uses: actions/checkout@v2

What sorts of browsers are supported ?

This tool uses the ChromeDP protocol to run the tests inside a Chrome browser. So Chrome or any blink-based browser will work.

Why not firefox ?

Great question. The initial idea was to use a Selenium API and drive any browser to run the tests. But unfortunately, geckodriver does not support the ability to capture console logs - https://github.com/mozilla/geckodriver/issues/284. Hence, the shift to use the ChromeDP protocol circumvents the need to have any external driver binary and just have a browser installed in the machine.

A tip on coverage data using go 1.20 or later:

Code coverage changes introduced in go 1.20 produce multiple coverage data files in binary format.

In wasmbrowsertest, file system operations for coverage files occur via HTTP API calls.

Prefer using -test.gocoverdir=/path/to/coverage instead of -test.coverprofile=coverage.out when coverage data is needed. This will prevent http api calls that would read all the coverage data files and write the larger coverage.out file.

In a subsequent step, use go tool covdata -i /path/to/coverage -o coverage.out or similar to process coverage data files into the desired output format. An additional benefit is that multiple test coverage runs that write their data to the same coverage directory can be merged together with this command.

Errors

total length of command line and environment variables exceeds limit

If the error total length of command line and environment variables exceeds limit appears, then the current environment variables' total size has exceeded the maximum when executing Go Wasm binaries.

To resolve this issue, install cleanenv and use it to prefix your command.

For example, if these commands are used:

export GOOS=js GOARCH=wasm
go test -cover ./...

The new commands should be the following:

go install github.com/agnivade/wasmbrowsertest/cmd/cleanenv@latest

export GOOS=js GOARCH=wasm
cleanenv -remove-prefix GITHUB_ -- go test -cover ./...

The cleanenv command above removes all environment variables prefixed with GITHUB_ before running the command after the --. The -remove-prefix flag can be repeated multiple times to remove even more environment variables.