fmdiff: modernize

Closes Homebrew/homebrew#37662.

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

Formula/fmdiff.rb

@@ -1,14 +1,27 @@
-require 'formula'
-
 class Fmdiff < Formula
-  homepage 'http://www.defraine.net/~brunod/fmdiff/'
-  url 'http://bruno.defraine.net/fmdiff/fmscripts-20120813.tar.gz'
-  sha1 'a5342820893f61b29e1060527cc722ef51574911'
+  homepage "https://www.defraine.net/~brunod/fmdiff/"
+  url "http://bruno.defraine.net/fmdiff/fmscripts-20120813.tar.gz"
+  sha256 "7312654040acc29787c15fb2b6d53abe0a397fb9faec6bf43398d25bb31f38ee"
 
-  head 'http://soft.vub.ac.be/svn-gen/bdefrain/fmscripts/', :using => :svn
+  head "http://soft.vub.ac.be/svn-gen/bdefrain/fmscripts/", :using => :svn
 
   def install
-  system "make"
-  system "make", "DESTDIR=#{bin}", "install"
+    system "make"
+    system "make", "DESTDIR=#{bin}", "install"
+  end
+
+  test do
+    ENV.prepend_path "PATH", testpath
+
+    # dummy filemerge script
+    (testpath/"filemerge").write <<-EOS.undent
+      #!/bin/sh
+      echo "it works"
+    EOS
+
+    chmod 0744, testpath/"filemerge"
+    touch "test"
+
+    assert_match(/it works/, shell_output("#{bin}/fmdiff test test"))
   end
 end