Recently, I was setting up a Github Action on my dice repository. I wanted to ensure that 2 things:

1. When a pull request is made into the main branch, that pull request built successfully and passed all unit tests.
2. After all unit tests passed, the total coverage of the unit tests for the entire project should be above 90%.

Go makes the first bullet point incredibly easy! go build ./... and go test ./... (or some variation of) are easy to run as part of the CI process using Github Action’s actions/setup-go@v6 action and choosing your go version/s. Go also provides the argument -coverprofile=<filename> that can be set in the go test command which will produce a coverage report of the desired filename. For example go test ./... -coverprofile=coverage.out will produce a coverage.out file in the root directory after running the tests which will have all the information about unit test coverage for the entire project. Go then provides a go tool cover -func=<filename> tool and command that can be used to get a breakdown of the coverage for each method in the project as well as the total test coverage on the last line (this is important!). For clarity, here’s an example output of running go tool cover -func=./out/coverage.out on my dice project:

github.com/abrhoda/dice/ast.go:11:	walk		72.2%
github.com/abrhoda/dice/parser.go:14:	NewParser	100.0%
github.com/abrhoda/dice/parser.go:30:	astFromTokens	96.7%
github.com/abrhoda/dice/parser.go:78:	Parse		100.0%
github.com/abrhoda/dice/scanner.go:14:	peekByte	100.0%
github.com/abrhoda/dice/scanner.go:22:	readByte	100.0%
github.com/abrhoda/dice/scanner.go:32:	isWhiteSpace	100.0%
github.com/abrhoda/dice/scanner.go:36:	isDigit		100.0%
github.com/abrhoda/dice/scanner.go:40:	isDiceCharacter	100.0%
github.com/abrhoda/dice/scanner.go:44:	isOperator	100.0%
github.com/abrhoda/dice/scanner.go:49:	isValidByte	100.0%
github.com/abrhoda/dice/scanner.go:55:	readToken	100.0%
github.com/abrhoda/dice/token.go:25:	evaluate	100.0%
total:					(statements)	95.4%

For my Github Action, I wanted to use this output of go tool cover -func=<filename> to get the total unit test coverage percentage and ensure that it is above a threshold. To do this, I wrote the following little bahs script:

cd "$(dirname "$0")"

main() {
  cd "$(pwd)/.."

  # TOTAL will be a decimal %
  TOTAL=$(go tool cover -func="$1" | grep total | awk '{print substr($3, 1, length($3)-1)}')
  

  if [[ `echo "$TOTAL $2" | awk '{print ($1 > $2)}'` == 1 ]];then
    echo "$TOTAL is greater than $2"
    return 0
  else
    echo "$TOTAL is less than $2"
    return 1
  fi
}

main "$@"

This script is invoked by running bash ./script/coverage_threshold.bash <coverage threshold> <minimum threshold percentage>. My Github Action has a hardcoded filename of ./out/coverage/out where a previous step in my Github Action writes the coverage file. The Github Action also sets a minimum threshold percentage of 90.0 percent in the environment. These are arguments $1 and $2 respectively. TOTAL in the script calls the go tool cover -func="$1" which prints the unit test coverage for each function with the last line being the projects total unit test coverage percentage, as mentioned above. It then uses grep to grab the line where the word “total” appears and pass that line into awk. awk then grabs the 3rd chunk (split by whitespace) which is the percent and returns the chunk as a number, without the % sign. This is stored in a variable called TOTAL. TOTAL and $2 (minimum threshold) are then echoed and passed into awk which compares them. If $TOTAL is more then $2, 0 is returned. Otherwise, 1 is returned. This follows the expected standard of a zero exit code meaning success and an exit code of non-zero to indicate a failure.

Notes:

1. go tool cover also provides an html view that can be used to view coverage of each file by line in an html view. While in the html view, text in green indicates that the line is covered by a test, text in red indicates that the line is not coverage by a test, and gray indicates that the line/text is ignored. What I have noticed though is that this tool considers a line covered if a single statement on the line is called. This means that a compound if booleanStatement1 || booleanStatement2 {} covered even if only booleanStatement1 is used in your tests and is always true. That means that, although booleanStatement2 is never evaluated in your tests due to booleanStatement1 always being true, this line will be green and considered covered.

2. This script may produce unexpected results if a file within the project has a filename of total or a function with the name total. This is because of the grep total line. In my dice project, this works as intended because total is not a filename or a function. Just a word of caution if you use this script and your project contains a filename or function with the name total.

Github Action link of this in action: go.yaml and the Makefile that it references.