Tests for the real data-path error, an empty data path, and a crypto/rand failure

cmd/fejkdata/main_test.go

@@ -355,3 +355,10 @@ func TestRunUnknownFlagIsNamedByRune(t *testing.T) {
 		t.Errorf("run(-ä) = %d, %q, want the flag named whole", code, errb)
 	}
 }
+
+func TestRunEmptyDataPathIsNamed(t *testing.T) {
+	code, _, errb := runOut("--data-path=", "sv_SE.word")
+	if code != 1 || !strings.Contains(errb, "empty") {
+		t.Errorf("run(--data-path=) = %d, %q, want the empty path named", code, errb)
+	}
+}

fejkdata_test.go

@@ -1,8 +1,11 @@
 package fejkdata
 
 import (
+	"errors"
+	"io/fs"
 	"strings"
 	"testing"
+	"testing/fstest"
 )
 
 // newGenerator creates a generator over a single data directory, failing on
@@ -38,8 +41,25 @@ func fake(t *testing.T, f *Generator, path string) string {
 
 func TestNewMissingDirectory(t *testing.T) {
 	_, err := New(WithoutShippedData(), WithDataPath("data/de_DE"))
-	if err == nil || !strings.Contains(err.Error(), "de_DE") {
+	if err == nil || !strings.Contains(err.Error(), "de_DE") || !errors.Is(err, fs.ErrNotExist) {
-		t.Fatalf("New(missing) error = %v, want it to name the path", err)
+		t.Fatalf("New(missing) error = %v, want the real error, naming the path", err)
+	}
+}
+
+func TestNewRejectsAnEmptyDataPath(t *testing.T) {
+	_, err := New(WithoutShippedData(), WithDataPath(""))
+	if err == nil || !strings.Contains(err.Error(), "empty") {
+		t.Fatalf("New(WithDataPath(\"\")) = %v, want the empty path named", err)
+	}
+}
+
+func TestNewReportsAnEntropyFailure(t *testing.T) {
+	saved := randomBytes
+	randomBytes = func([]byte) (int, error) { return 0, errors.New("no entropy") }
+	defer func() { randomBytes = saved }()
+	_, err := New(WithoutShippedData(), WithDataFS(fstest.MapFS{"w.json": {Data: []byte(`"x"`)}}))
+	if err == nil || !strings.Contains(err.Error(), "no entropy") {
+		t.Fatalf("New() without entropy = %v, want the failure reported", err)
 	}
 }
 

template_test.go

@@ -8,7 +8,13 @@ import (
 )
 
 // engine builds a seeded generator with no loaded categories, for rendering tests.
-func engine(seed uint64) *Generator { return &Generator{rand: newRand(seed, true)} }
+func engine(seed uint64) *Generator {
+	s, err := newRand(seed, true)
+	if err != nil {
+		panic(err)
+	}
+	return &Generator{rand: s}
+}
 
 // parse unmarshals a JSON template fragment into its dynamic form.
 func parse(t *testing.T, s string) any {