+ Fail gracefully when expectation used outside of it.

[git-p4: depot-paths = "//src/minitest/dev/": change = 11568]

lib/minitest/spec.rb

@@ -14,6 +14,7 @@ def #{new_name} *args
 
     Minitest::Expectation.class_eval <<-EOM, __FILE__, __LINE__ + 1
       def #{new_name} *args
+        raise "Calling ##{new_name} outside of test." unless ctx
         case
         when #{!!dont_flip} then
           ctx.#{meth}(target, *args)

test/minitest/test_minitest_spec.rb

@@ -511,12 +511,30 @@ def assert_triggered expected = "blah", klass = Minitest::Assertion
 
     it "can NOT use must_equal in a thread. It must use expect in a thread" do
       skip "N/A" if ENV["MT_NO_EXPECTATIONS"]
-      assert_raises NoMethodError do
+      assert_raises RuntimeError do
         capture_io do
           Thread.new { (1 + 1).must_equal 2 }.join
         end
       end
     end
+
+    it "fails gracefully when expectation used outside of `it`" do
+      skip "N/A" if ENV["MT_NO_EXPECTATIONS"]
+
+      @assertion_count += 1
+
+      e = assert_raises RuntimeError do
+        capture_io do
+          Thread.new { # forces ctx to be nil
+            describe("woot") do
+              (1 + 1).must_equal 2
+            end
+          }.join
+        end
+      end
+
+      assert_equal "Calling #must_equal outside of test.", e.message
+    end
   end
 
   it "needs to verify throw" do