zshdb: modernize + test

Closes Homebrew/homebrew#35416.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>

Formula/zshdb.rb

@@ -1,17 +1,15 @@
-require 'formula'
-
 class Zshdb < Formula
-  homepage 'https://github.com/rocky/zshdb'
-  url 'https://downloads.sourceforge.net/project/bashdb/zshdb/0.08/zshdb-0.08.tar.bz2'
-  sha1 '29f860d0130debe6a966ee1e12f2f3046c78897b'
+  homepage "https://github.com/rocky/zshdb"
+  url "https://downloads.sourceforge.net/project/bashdb/zshdb/0.08/zshdb-0.08.tar.bz2"
+  sha1 "29f860d0130debe6a966ee1e12f2f3046c78897b"
 
   head do
-    url 'https://github.com/rocky/zshdb.git'
+    url "https://github.com/rocky/zshdb.git"
     depends_on "autoconf" => :build
     depends_on "automake" => :build
   end
 
-  depends_on 'zsh'
+  depends_on "zsh"
 
   def install
     if build.head?
@@ -22,6 +20,14 @@ class Zshdb < Formula
     system "./configure", "--disable-dependency-tracking",
                           "--prefix=#{prefix}",
                           "--with-zsh=#{HOMEBREW_PREFIX}/bin/zsh"
-    system "make install"
+    system "make", "install"
+  end
+
+  test do
+    require "open3"
+    Open3.popen3("#{bin}/zshdb -c 'echo test'") do |stdin, stdout, _|
+      stdin.write "exit\n"
+      !!(stdout.read =~ /That's all, folks/)
+    end
   end
 end