Add convenience methods for executing commands

This follows a similar approach to the Path
helper and extracts methods for each call to
Exec so that Provider and its specs are much
simpler.

I also added stubs for Exec to spec_helper.rb
so that we don't execute commands in the
tests, except where they're explicitly
unstubbed to unit test .execute and .capture.

lib/zz/commands/provision.rb

@@ -2,20 +2,8 @@ module ZZ
   module Provision
     class << self
       def execute(args)
-        install_chef unless chef_installed?
-        run_chef
-      end
-
-      def install_chef
-        Exec.execute("curl -sL #{ZZ::Path.chef_installer} | sudo bash")
-      end
-
-      def chef_installed?
-        Exec.execute("which chef-solo")
-      end
-
-      def run_chef
-        Exec.execute("chef-solo --config #{ZZ::Path.chef_config}")
+        Exec.install_chef unless Exec.chef_installed?
+        Exec.run_chef
       end
 
       def name

lib/zz/exec.rb

@@ -1,11 +1,25 @@
 module ZZ
   module Exec
-    def self.execute(command)
-      system(command)
-    end
+    class << self
+      def execute(command)
+        system(command)
+      end
+
+      def capture(command)
+        `#{command}`
+      end
+
+      def install_chef
+        execute("curl -sL #{Path.chef_installer} | sudo bash")
+      end
+
+      def chef_installed?
+        execute("which chef-solo")
+      end
 
-    def self.capture(command)
-      `#{command}`
+      def run_chef
+        execute("chef-solo --config #{Path.chef_config}")
+      end
     end
   end
 end

spec/spec_helper.rb

@@ -7,4 +7,9 @@
   config.disable_monkey_patching!
   config.formatter = :doc
   config.color = true
+
+  config.before do
+    allow(ZZ::Exec).to receive(:execute)
+    allow(ZZ::Exec).to receive(:capture)
+  end
 end

spec/zz/commands/provision_spec.rb

@@ -6,33 +6,21 @@
   end
 
   it "installs chef if it isn't already installed" do
-    allow(ZZ::Exec).to receive(:execute)
-      .with("which chef-solo").and_return(false)
-
-    expect(ZZ::Exec).to receive(:execute)
-      .with("curl -sL #{ZZ::Path.chef_installer} | sudo bash")
-
-    allow(ZZ::Exec).to receive(:execute)
+    allow(ZZ::Exec).to receive(:chef_installed?).and_return(false)
+    expect(ZZ::Exec).to receive(:install_chef)
 
     subject.execute([])
   end
 
   it "does not install chef if it's already installed" do
-    allow(ZZ::Exec).to receive(:execute)
-      .with("which chef-solo").and_return(true)
-
-    expect(ZZ::Exec).not_to receive(:execute)
-      .with("curl -sL #{ZZ::Path.chef_installer} } | sudo bash")
+    allow(ZZ::Exec).to receive(:chef_installed?).and_return(true)
+    expect(ZZ::Exec).not_to receive(:install_chef)
 
     subject.execute([])
   end
 
   it "runs chef" do
-    allow(ZZ::Exec).to receive(:execute)
-
-    expect(ZZ::Exec).to receive(:execute)
-      .with("chef-solo --config #{ZZ::Path.chef_config}")
-
+    expect(ZZ::Exec).to receive(:run_chef)
     subject.execute([])
   end
 

spec/zz/exec_spec.rb

@@ -1,5 +1,9 @@
 RSpec.describe ZZ::Exec do
   describe ".execute" do
+    before do
+      allow(subject).to receive(:execute).and_call_original
+    end
+
     it "executes the command in a subprocess" do
       result = subject.execute("touch foo")
 
@@ -11,9 +15,42 @@
   end
 
   describe ".capture" do
+    before do
+      allow(subject).to receive(:capture).and_call_original
+    end
+
     it "executes the command and returns its output" do
       result = subject.capture("echo foo")
       expect(result).to eq("foo\n")
     end
   end
+
+  describe ".install_chef" do
+    it "curls the chef installer and runs it as root" do
+      expect(subject).to receive(:execute)
+        .with("curl -sL #{ZZ::Path.chef_installer} | sudo bash")
+
+      subject.install_chef
+    end
+  end
+
+  describe ".chef_installed?" do
+    it "returns whether chef-solo is installed" do
+      bool = double(:bool)
+
+      expect(subject).to receive(:execute)
+        .with("which chef-solo").and_return(bool)
+
+      expect(subject.chef_installed?).to eq(bool)
+    end
+  end
+
+  describe ".run_chef" do
+    it "runs chef with the path to its config" do
+      expect(subject).to receive(:execute)
+        .with("chef-solo --config #{ZZ::Path.chef_config}")
+
+      subject.run_chef
+    end
+  end
 end