test: set test flags from within an init to limit maximum test parallelism (#19575)

coderd/coderdtest/initflags.go

@@ -0,0 +1,55 @@
+package coderdtest
+
+import (
+	"flag"
+	"fmt"
+	"runtime"
+	"strconv"
+	"testing"
+)
+
+const (
+	// MaxTestParallelism is set to match our MakeFile's `make test` target.
+	MaxTestParallelism = 8
+)
+
+// init defines the default parallelism for tests, capping it to MaxTestParallelism.
+// Any user-provided value for -test.parallel will override this.
+func init() {
+	// Setup the test flags.
+	testing.Init()
+
+	// info is used for debugging panics in this init function.
+	info := "Resolve the issue in the file initflags.go"
+	_, file, line, ok := runtime.Caller(0)
+	if ok {
+		info = fmt.Sprintf("Resolve the issue in the file %s:%d", file, line)
+	}
+
+	// Lookup the test.parallel flag's value, and cap it to MaxTestParallelism. This
+	// all happens before `flag.Parse()`, so any user-provided value will overwrite
+	// whatever we set here.
+	par := flag.CommandLine.Lookup("test.parallel")
+	if par == nil {
+		// This should never happen. If you are reading this message because of a panic,
+		// just comment out the panic and add a `return` statement instead.
+		msg := "no 'test.parallel' flag found, unable to set default parallelism"
+		panic(msg + "\n" + info)
+	}
+
+	parValue, err := strconv.ParseInt(par.Value.String(), 0, 64)
+	if err != nil {
+		// This should never happen, but if it does, panic with a useful message. If you
+		// are reading this message because of a panic, that means the default value for
+		// -test.parallel is not an integer. A safe fix is to comment out the panic. This
+		// will assume the default value of '0', and replace it with MaxTestParallelism.
+		// Which is not ideal, but at least tests will run.
+		msg := fmt.Sprintf("failed to parse test.parallel: %v", err)
+
+		panic(msg + "\n" + info)
+	}
+
+	if parValue > MaxTestParallelism {
+		_ = par.Value.Set(fmt.Sprintf("%d", MaxTestParallelism))
+	}
+}