Add rspec for kernel extension. Update README to reflect label usage

Author: technicalpickles

README.md

@@ -32,7 +32,7 @@ Singed.output_directory = "tmp/slowness-exploration"
 If you are calling it in a loop, or with different variations, you can include a label on the filename:
 
 ```ruby
-flamegraph(label: "rspec") {
+flamegraph("rspec") {
   # your code here
 }
 ```

lib/singed/kernel_ext.rb

@@ -1,15 +1,15 @@
 module Kernel
-  def flamegraph(label = nil, open: true, ignore_gc: false, interval: 1000, &block)
+  def flamegraph(label = nil, open: true, ignore_gc: false, interval: 1000, io: $stdout, &block)
     fg = Singed::Flamegraph.new(label: label, ignore_gc: ignore_gc, interval: interval)
     result = fg.record(&block)
     fg.save
 
     if open
       # use npx, so we don't have to add it as a dependency
-      puts "🔥📈 #{'Captured flamegraph, opening with'.colorize(:bold).colorize(:red)}: #{fg.open_command}"
+      io.puts "🔥📈 #{'Captured flamegraph, opening with'.colorize(:bold).colorize(:red)}: #{fg.open_command}"
       fg.open
     else
-      puts "🔥📈 #{'Captured flamegraph to file'.colorize(:bold).colorize(:red)}: #{fg.filename}"
+      io.puts "🔥📈 #{'Captured flamegraph to file'.colorize(:bold).colorize(:red)}: #{fg.filename}"
     end
 
     result

spec/singed/kernel_ext_spec.rb

@@ -0,0 +1,60 @@
+describe Kernel, "extension" do
+  let(:flamegraph) { 
+    instance_double(Singed::Flamegraph)
+  }
+
+  before do
+    allow(Singed::Flamegraph).to receive(:new).and_return(flamegraph)
+    allow(flamegraph).to receive(:record)
+    allow(flamegraph).to receive(:save)
+    allow(flamegraph).to receive(:open)
+    allow(flamegraph).to receive(:open_command)
+    allow(flamegraph).to receive(:filename)
+  end
+
+  let(:io) { StringIO.new }
+
+  it "works without any arguments" do
+    # * except what's needed to test
+    # note: use Object.new to get the actual flamegraph kernel extension, instead of the rspec-specific flamegraph
+    Object.new.flamegraph io: io do
+    end
+
+    expect(Singed::Flamegraph).to have_received(:new).with(label: nil, ignore_gc: false, interval: 1000)
+  end
+
+  it "works with explicit arguments" do
+    # note: use Object.new to get the actual flamegraph kernel extension, instead of the rspec-specific flamegraph
+    Object.new.flamegraph 'yellowjackets', ignore_gc: true, interval: 2000, io: io do
+    end
+
+    expect(Singed::Flamegraph).to have_received(:new).with(label: 'yellowjackets', ignore_gc: true, interval: 2000)
+  end
+
+  context "default" do
+    it "opens" do
+      Object.new.flamegraph open: true, io: io do
+      end
+      
+      expect(flamegraph).to have_received(:open)
+    end
+  end
+
+  context "open: true" do
+    it "opens" do
+      Object.new.flamegraph open: true, io: io do
+      end
+
+      expect(flamegraph).to have_received(:open)
+    end
+  end
+
+  context "open: false" do
+    it "doesn't open" do
+      Object.new.flamegraph open: false, io: io do
+      end
+
+      expect(flamegraph).to_not have_received(:open)
+    end
+  end
+end