fix: make miro testdir resolution explicit based on config

internal/config/config.go

@@ -1,6 +1,7 @@
 package config
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"os"
@@ -13,10 +14,6 @@ type Config struct {
 }
 
 type tomlConfig struct {
-	Miro tomlMiroConfig `toml:"miro"`
-}
-
-type tomlMiroConfig struct {
 	TestDir string `toml:"test_dir"`
 }
 
@@ -24,15 +21,37 @@ type tomlMiroConfig struct {
 func ReadConfig(path string) (Config, error) {
 	var raw tomlConfig
 
-	_, err := toml.DecodeFile(path, &raw)
+	meta, err := toml.DecodeFile(path, &raw)
 	if err != nil {
 		if errors.Is(err, os.ErrNotExist) {
 			return Config{}, err
 		}
 		return Config{}, fmt.Errorf("failed to read %s: %v", path, err)
 	}
+	if !meta.IsDefined("test_dir") {
+		return Config{}, fmt.Errorf("failed to read %s: missing required test_dir", path)
+	}
+	if raw.TestDir == "" {
+		return Config{}, fmt.Errorf("failed to read %s: empty test_dir", path)
+	}
 
 	return Config{
-		TestDir: raw.Miro.TestDir,
+		TestDir: raw.TestDir,
 	}, nil
 }
+
+// WriteConfig writes miro.toml.
+func WriteConfig(path string, cfg Config) error {
+	if cfg.TestDir == "" {
+		return errors.New("empty test_dir")
+	}
+
+	var buf bytes.Buffer
+	if err := toml.NewEncoder(&buf).Encode(tomlConfig{
+		TestDir: cfg.TestDir,
+	}); err != nil {
+		return fmt.Errorf("failed to encode %s: %v", path, err)
+	}
+
+	return os.WriteFile(path, buf.Bytes(), 0o644)
+}

internal/config/config_test.go

@@ -1,8 +1,10 @@
 package config
 
 import (
+	"errors"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 )
 
@@ -11,36 +13,63 @@ func TestReadConfig(t *testing.T) {
 		name        string
 		content     string
 		wantDir     string
-		wantReadErr bool
+		wantErr     string
+		wantMissing bool
 	}{
 		{
 			name:    "with test dir",
-			content: "[miro]\ntest_dir = \"custom/suite\"\n",
+			content: "test_dir = \"custom/suite\"\n",
 			wantDir: "custom/suite",
 		},
 		{
-			name:    "without test dir",
-			content: "[miro]\n",
+			name:    "legacy miro table",
+			content: "[miro]\ntest_dir = \"custom/suite\"\n",
+			wantErr: "missing required test_dir",
 		},
 		{
-			name:        "invalid toml",
-			content:     "[miro]\ntest_dir = [\n",
-			wantReadErr: true,
+			name:    "without test dir",
+			content: "",
+			wantErr: "missing required test_dir",
+		},
+		{
+			name:    "empty test dir",
+			content: "test_dir = \"\"\n",
+			wantErr: "empty test_dir",
+		},
+		{
+			name:    "invalid toml",
+			content: "test_dir = [\n",
+			wantErr: "failed to read",
+		},
+		{
+			name:        "missing file",
+			wantMissing: true,
 		},
 	}
 
 	for _, tt := range tests {
 		t.Run(tt.name, func(t *testing.T) {
 			path := filepath.Join(t.TempDir(), "miro.toml")
-			if err := os.WriteFile(path, []byte(tt.content), 0o644); err != nil {
-				t.Fatalf("WriteFile() error = %v", err)
+			if !tt.wantMissing {
+				if err := os.WriteFile(path, []byte(tt.content), 0o644); err != nil {
+					t.Fatalf("WriteFile() error = %v", err)
+				}
 			}
 
 			got, err := ReadConfig(path)
-			if tt.wantReadErr {
+			if tt.wantMissing {
+				if !errors.Is(err, os.ErrNotExist) {
+					t.Fatalf("ReadConfig() error = %v, want os.ErrNotExist", err)
+				}
+				return
+			}
+			if tt.wantErr != "" {
 				if err == nil {
 					t.Fatal("ReadConfig() error = nil, want error")
 				}
+				if !strings.Contains(err.Error(), tt.wantErr) {
+					t.Fatalf("ReadConfig() error = %q, want substring %q", err.Error(), tt.wantErr)
+				}
 				return
 			}
 			if err != nil {
@@ -52,3 +81,31 @@ func TestReadConfig(t *testing.T) {
 		})
 	}
 }
+
+func TestWriteConfig(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "miro.toml")
+
+	if err := WriteConfig(path, Config{TestDir: "e2e"}); err != nil {
+		t.Fatalf("WriteConfig() error = %v", err)
+	}
+
+	got, err := os.ReadFile(path)
+	if err != nil {
+		t.Fatalf("ReadFile() error = %v", err)
+	}
+	if string(got) != "test_dir = \"e2e\"\n" {
+		t.Fatalf("config = %q, want %q", string(got), "test_dir = \"e2e\"\n")
+	}
+}
+
+func TestWriteConfigEmptyTestDirFails(t *testing.T) {
+	path := filepath.Join(t.TempDir(), "miro.toml")
+
+	err := WriteConfig(path, Config{})
+	if err == nil {
+		t.Fatal("WriteConfig() error = nil, want error")
+	}
+	if err.Error() != "empty test_dir" {
+		t.Fatalf("WriteConfig() error = %q, want %q", err.Error(), "empty test_dir")
+	}
+}