Add Runtime#available?

lib/execjs/runtime.rb

@@ -20,6 +20,12 @@ module ExecJS
       end
     end
 
+    def available?
+      command = @command.split(/\s+/).first
+      `which #{command}`
+      $? == 0
+    end
+
     protected
       def compile(source)
         runner_source.sub('#{source}', source)

test/test_execjs.rb

@@ -9,4 +9,12 @@ class TestExecJS < Test::Unit::TestCase
   def test_eval
     assert_equal ["red", "yellow", "blue"], ExecJS.eval("'red yellow blue'.split(' ')")
   end
+
+  def test_runtime_available
+    runtime = ExecJS::Runtime.new(:command => "nonexistent")
+    assert_equal false, runtime.available?
+
+    runtime = ExecJS::Runtime.new(:command => "ruby")
+    assert_equal true, runtime.available?
+  end
 end

test/test_runtimes.rb

@@ -39,34 +39,26 @@ module TestRuntime
   end
 end
 
-class TestJSCRuntime < Test::Unit::TestCase
+def test_runtime(name)
+  runtime = ExecJS::Runtimes.const_get(name)
+  if runtime.available?
+    Class.new(Test::Unit::TestCase) do
+      (class << self; self end).send(:define_method, :name) do
+        "#{name}Test"
+      end
+
       include TestRuntime
 
-  def setup
-    @runtime = ExecJS::Runtimes::JSC
+      define_method(:setup) do
+        instance_variable_set(:@runtime, runtime)
+      end
+    end
+  else
+    warn "#{name} runtime is unavailable, skipping"
   end
 end
 
-class TestNodeRuntime < Test::Unit::TestCase
-  include TestRuntime
-
-  def setup
-    @runtime = ExecJS::Runtimes::Node
-  end
-end
-
-class TestSpidermonkeyRuntime < Test::Unit::TestCase
-  include TestRuntime
-
-  def setup
-    @runtime = ExecJS::Runtimes::Spidermonkey
-  end
-end
-
-class TestV8Runtime < Test::Unit::TestCase
-  include TestRuntime
-
-  def setup
-    @runtime = ExecJS::Runtimes::V8
-  end
-end
+test_runtime :JSC
+test_runtime :Node
+test_runtime :Spidermonkey
+test_runtime :V8