Added golines playground

cmds/golines/format_test.go

@@ -0,0 +1,45 @@
+package main
+
+import (
+	"go/parser"
+	"go/token"
+	"strings"
+	"testing"
+)
+
+func TestFormatWidths(t *testing.T) {
+	source := `package main
+func main() {
+ println("first argument", "second argument", "third argument", "fourth argument")
+}
+`
+	var narrow, wide string
+	for width := 40; width <= 180; width += 5 {
+		output, err := formatSource(source, width)
+		if err != nil {
+			t.Fatalf("width %d: %v", width, err)
+		}
+		if _, err := parser.ParseFile(token.NewFileSet(), "output.go", output, parser.AllErrors); err != nil {
+			t.Fatalf("width %d produced invalid Go: %v", width, err)
+		}
+		if width == 40 {
+			narrow = string(output)
+		}
+		if width == 180 {
+			wide = string(output)
+		}
+	}
+	if strings.Count(narrow, "\n") <= strings.Count(wide, "\n") {
+		t.Fatal("narrow width did not split the call")
+	}
+}
+
+func TestInvalidSource(t *testing.T) {
+	if _, err := formatSource("package main\nfunc {", 100); err == nil {
+		t.Fatal("expected a syntax error")
+	}
+	// A failed edit must not prevent subsequent formatting.
+	if _, err := formatSource("package main\nfunc main() {}", 100); err != nil {
+		t.Fatal(err)
+	}
+}