tests: Reimplement test harness in Go

And make it run in parallell

shell.nix

@@ -16,16 +16,11 @@
   )
 }:
 
-let
-  pythonEnv = pkgs.python3.withPackages (_: [ ]);
-
-in
 pkgs.mkShell {
   buildInputs = [
     pkgs.nix-prefetch-git
     pkgs.nixpkgs-fmt
     pkgs.go
     pkgs.gomod2nix
-    pythonEnv
   ];
 }

tests/Makefile

@@ -1,2 +1,2 @@
 all:
-	python ./run.py
+	go run ./run.go

tests/run.go

@@ -0,0 +1,122 @@
+package main
+
+import (
+	"bufio"
+	"bytes"
+	"fmt"
+	"io"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"sync"
+)
+
+var cwd = func() string {
+	cwd, err := os.Getwd()
+	if err != nil {
+		panic(err)
+	}
+	return cwd
+}()
+
+type testError struct {
+	testDir string
+	stdout  bytes.Buffer
+	stderr  bytes.Buffer
+}
+
+func runProcess(prefix string, command string, args ...string) error {
+	fmt.Println(fmt.Sprintf("%s: Executing %s %s", prefix, command, args))
+
+	cmd := exec.Command(command, args...)
+
+	stdoutReader, err := cmd.StdoutPipe()
+	if err != nil {
+		return err
+	}
+
+	stderrReader, err := cmd.StderrPipe()
+	if err != nil {
+		return err
+	}
+
+	done := make(chan struct{})
+
+	go func() {
+		reader := io.MultiReader(stdoutReader, stderrReader)
+		scanner := bufio.NewScanner(reader)
+		for scanner.Scan() {
+			line := scanner.Bytes()
+			fmt.Println(fmt.Sprintf("%s: %s", prefix, line))
+		}
+		done <- struct{}{}
+	}()
+
+	err = cmd.Start()
+	if err != nil {
+		return err
+	}
+
+	<-done
+
+	return cmd.Wait()
+}
+
+func runTest(testDir string) error {
+	rootDir := filepath.Join(cwd, "..")
+
+	cmdPath := filepath.Join(rootDir, "gomod2nix")
+	err := runProcess(testDir, cmdPath, "--dir", testDir, "--outdir", testDir)
+	if err != nil {
+		return err
+	}
+
+	buildExpr := fmt.Sprintf("with (import <nixpkgs> { overlays = [ (import %s/overlay.nix) ]; }); callPackage ./%s {}", rootDir, testDir)
+	err = runProcess(testDir, "nix-build", "--no-out-link", "--expr", buildExpr)
+	if err != nil {
+		return err
+	}
+
+	return nil
+}
+
+func main() {
+
+	files, err := os.ReadDir(".")
+	if err != nil {
+		panic(err)
+	}
+
+	testDirs := []string{}
+	for _, f := range files {
+		if f.IsDir() {
+			testDirs = append(testDirs, f.Name())
+		}
+	}
+
+	var wg sync.WaitGroup
+	cmdErrChan := make(chan error)
+	for _, testDir := range testDirs {
+		testDir := testDir
+		fmt.Println(fmt.Sprintf("Running test for: '%s'", testDir))
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			err := runTest(testDir)
+			if err != nil {
+				cmdErrChan <- err
+			}
+		}()
+	}
+
+	go func() {
+		wg.Wait()
+		close(cmdErrChan)
+	}()
+
+	for cmdErr := range cmdErrChan {
+		fmt.Println(fmt.Sprintf("Test for '%s' failed:", cmdErr))
+		os.Exit(1)
+	}
+
+}

tests/run.py

@@ -1,30 +0,0 @@
-#!/usr/bin/env python
-import subprocess
-import os.path
-import sys
-
-
-if __name__ == '__main__':
-    script_dir = os.path.dirname(os.path.abspath(__file__))
-    root_dir = os.path.dirname(script_dir)
-
-    cmd = os.path.join(root_dir, "gomod2nix")
-
-    def run(directory):
-        print(f"Running {directory}")
-
-        subprocess.run([cmd, "--dir", directory, "--outdir", directory], check=True)
-
-        build_expr = ("""
-        with (import <nixpkgs> { overlays = [ (import %s/overlay.nix) ]; }); callPackage %s {}
-        """.replace("\n", " ") % (root_dir, directory))
-        subprocess.run(["nix-build", "--expr", build_expr], check=True)
-
-    for f in os.listdir(script_dir):
-
-        d = os.path.join(script_dir, f)
-        if os.path.isdir(d):
-            try:
-                run(d)
-            except Exception:
-                sys.stderr.write(f"Error running {d}\n")