Test internal/drawstate and the module packages each package may import

imports_test.go

@@ -0,0 +1,66 @@
+package fejkdata
+
+import (
+	"errors"
+	"go/build"
+	"io/fs"
+	"path/filepath"
+	"slices"
+	"strings"
+	"testing"
+)
+
+// TestPackageImports holds each package in the module to the module packages it may import.
+func TestPackageImports(t *testing.T) {
+	const module = "github.com/larvit/fejkdata"
+	allowed := map[string][]string{
+		".":                  {"internal/drawstate"},
+		"cmd/fejkdata":       {"."},
+		"internal/drawstate": nil,
+	}
+	seen := map[string]bool{}
+	err := filepath.WalkDir(".", func(dir string, d fs.DirEntry, err error) error {
+		if err != nil || !d.IsDir() {
+			return err
+		}
+		if dir != "." && (strings.HasPrefix(d.Name(), ".") || d.Name() == "testdata") {
+			return filepath.SkipDir
+		}
+		pkg, err := build.ImportDir(dir, 0)
+		var noGo *build.NoGoError
+		if errors.As(err, &noGo) {
+			return nil
+		}
+		if err != nil {
+			return err
+		}
+		dir = filepath.ToSlash(dir)
+		seen[dir] = true
+		may, listed := allowed[dir]
+		if !listed {
+			t.Errorf("package %s is not listed: add the module packages it may import", dir)
+			return nil
+		}
+		for _, imp := range slices.Concat(pkg.Imports, pkg.TestImports, pkg.XTestImports) {
+			if imp != module && !strings.HasPrefix(imp, module+"/") {
+				continue
+			}
+			rel := strings.TrimPrefix(strings.TrimPrefix(imp, module), "/")
+			if rel == "" {
+				rel = "."
+			}
+			if rel != dir && !slices.Contains(may, rel) {
+				t.Errorf("package %s imports %s, which its list does not allow", dir, rel)
+			}
+		}
+		return nil
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+	for dir := range allowed {
+		if !seen[dir] {
+			t.Errorf("listed package %s does not exist", dir)
+		}
+	}
+}