libsvm: add test

Add simple test (adapated from the test in the tinysvm formula). Also
modernize the formula:
- remove `require 'formula'`
- use sha256
- use double quotes

Closes Homebrew/homebrew#39019.

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

Formula/libsvm.rb

@@ -1,9 +1,7 @@
-require 'formula'
-
 class Libsvm < Formula
-  homepage 'http://www.csie.ntu.edu.tw/~cjlin/libsvm/'
-  url 'http://www.csie.ntu.edu.tw/~cjlin/libsvm/libsvm-3.20.tar.gz'
-  sha1 '6902c22afadc70034c0d1c0e25455df10fb01eaf'
+  homepage "http://www.csie.ntu.edu.tw/~cjlin/libsvm/"
+  url "http://www.csie.ntu.edu.tw/~cjlin/libsvm/libsvm-3.20.tar.gz"
+  sha256 "0f122480bef44dec4df6dae056f468c208e4e08c00771ec1b6dae2707fd945be"
 
   bottle do
     cellar :any
@@ -21,4 +19,23 @@ class Libsvm < Formula
     system "install_name_tool", "-id", "#{lib}/libsvm.2.dylib", "#{lib}/libsvm.2.dylib"
     include.install "svm.h"
   end
+
+  test do
+    (testpath/"train_classification.txt").write <<-EOS.undent
+    +1 201:1.2 3148:1.8 3983:1 4882:1
+    -1 874:0.3 3652:1.1 3963:1 6179:1
+    +1 1168:1.2 3318:1.2 3938:1.8 4481:1
+    +1 350:1 3082:1.5 3965:1 6122:0.2
+    -1 99:1 3057:1 3957:1 5838:0.3
+    EOS
+
+    (testpath/"train_regression.txt").write <<-EOS.undent
+    0.23 201:1.2 3148:1.8 3983:1 4882:1
+    0.33 874:0.3 3652:1.1 3963:1 6179:1
+    -0.12 1168:1.2 3318:1.2 3938:1.8 4481:1
+    EOS
+
+    system "#{bin}/svm-train", "-s", "0", "train_classification.txt"
+    system "#{bin}/svm-train", "-s", "3", "train_regression.txt"
+  end
 end