Fix Snapshot#crop to not burn when height > line count

app/models/snapshot.rb

@@ -11,6 +11,7 @@ class Snapshot
   end
 
   def crop(width, height)
+    height = [height, lines.size].min
     new_lines = lines.drop(lines.size - height).map { |line| line.crop(width) }
     self.class.new(new_lines)
   end

spec/models/snapshot_spec.rb

@@ -23,22 +23,48 @@ describe Snapshot do
   describe '#crop' do
     let(:snapshot) { Snapshot.new(lines) }
     let(:lines) { [line_1, line_2, line_3] }
-    let(:line_1) { double('line_1', :crop => nil) }
+    let(:line_1) { double('line_1', :crop => cropped_line_1) }
     let(:line_2) { double('line_2', :crop => cropped_line_2) }
     let(:line_3) { double('line_3', :crop => cropped_line_3) }
+    let(:cropped_line_1) { double('cropped_line_1') }
     let(:cropped_line_2) { double('cropped_line_2') }
     let(:cropped_line_3) { double('cropped_line_3') }
+    let(:width) { 3 }
 
-    it 'crops the last "height" lines' do
-      snapshot.crop(3, 2)
+    subject { snapshot.crop(width, height) }
 
-      expect(line_1).to_not have_received(:crop)
-      expect(line_2).to have_received(:crop).with(3)
-      expect(line_3).to have_received(:crop).with(3)
+    context "when height is lower than lines count" do
+      let(:height) { 2 }
+
+      it 'crops the last "height" lines' do
+        subject
+
+        expect(line_1).to_not have_received(:crop)
+        expect(line_2).to have_received(:crop).with(3)
+        expect(line_3).to have_received(:crop).with(3)
+      end
+
+      it 'returns a new Snapshot with last 2 lines cropped' do
+        expect(subject).to eq(Snapshot.new([cropped_line_2, cropped_line_3]))
+      end
     end
 
-    it 'returns a new Snapshot with cropped lines' do
-      expect(snapshot.crop(3, 2)).to eq(Snapshot.new([cropped_line_2, cropped_line_3]))
+    context "when height is equal to lines count" do
+      let(:height) { 3 }
+
+      it 'returns a new Snapshot with all lines cropped' do
+        expect(subject).to eq(Snapshot.new([cropped_line_1, cropped_line_2,
+                                            cropped_line_3]))
+      end
+    end
+
+    context "when height is greater than lines count" do
+      let(:height) { 4 }
+
+      it 'returns a new Snapshot with all lines cropped' do
+        expect(subject).to eq(Snapshot.new([cropped_line_1, cropped_line_2,
+                                            cropped_line_3]))
+      end
     end
   end
 end