Add tests for Result#call implementations

spec/pending_result_spec.cr

@@ -5,6 +5,21 @@ def new_pending_result(example : Spectator::Example? = nil)
 end
 
 describe Spectator::PendingResult do
+  describe "#call" do
+    it "invokes #pending on an instance" do
+      spy = ResultCallSpy.new
+      new_pending_result.call(spy)
+      spy.pending?.should be_truthy
+    end
+
+    it "passes itself" do
+      spy = ResultCallSpy.new
+      result = new_pending_result
+      result.call(spy)
+      spy.pending.should eq(result)
+    end
+  end
+
   describe "#example" do
     it "is the expected value" do
       example = PassingExample.create