fix Dataset specs (check output)

Author: ievgrafov

spec/dataset_spec.rb

@@ -131,7 +131,7 @@
     end
   end
 
-  context 'updating' do
+  context 'safe update' do
     before do
       x = (0..10).to_a
       y = x.map { |xx| Math.exp(-xx) }
@@ -186,20 +186,20 @@
     end
 
     it 'should update an option of existing object' do
-      @ds.lw!(3)
+      expect(@ds.lw!(3)).to equal(@ds)
       expect(@ds.lw).to eql(3)
       @ds.pt = 8
       expect(@ds.pt).to eql(8)
     end
 
     it 'should update several options of existing object at once via #options!' do
-      @ds.options!(lw: 3, pt: 8)
+      expect(@ds.options!(lw: 3, pt: 8)).to equal(@ds)
       expect(@ds.lw).to eql(3)
       expect(@ds.pt).to eql(8)
     end
 
     it 'should update several options of existing object at once via #update!' do
-      @ds.update!(lw: 3, pt: 8)
+      expect(@ds.update!(lw: 3, pt: 8)).to equal(@ds)
       expect(@ds.lw).to eql(3)
       expect(@ds.pt).to eql(8)
     end
@@ -211,7 +211,7 @@
       x1 = (11..15).to_a
       y1 = x1.map { |xx| Math.exp(-xx) }
       @ds.plot(options0)
-      @ds.update!([x1, y1])
+      expect(@ds.update!([x1, y1])).to equal(@ds)
       @ds.plot(options1)
       expect(same_images?(*paths)).to be_falsey
     end
@@ -220,7 +220,7 @@
       x1 = (11..15).to_a
       y1 = x1.map { |xx| Math.exp(-xx) }
       size_before = File.size(@ds_file.data.to_s[1..-2])
-      @ds_file.update!([x1, y1])
+      expect(@ds_file.update!([x1, y1])).to equal(@ds_file)
       size_after = File.size(@ds_file.data.to_s[1..-2])
       expect(size_after).to be > size_before
     end