Fixes #493 Capture exit exception for reference

This stores any exit exception that may have occurred. The idea is to
expose this exception to the user supplied ```at_exit``` block.

```ruby
SimpleCov.at_exit do
  if SimpleCov.exit_exception
    # Do something or nothing due to an exception
  else
    # Do something or nothing due to no exception
  end
end
```

Another method was added: ```exit_status_from_exception``` to reduce the
logic in the at_exit block. I am not sure if it's worth adding this
method though. There is still opportunity to refactor the ```at_exit```
block. I first attempted to refactor the @exit_status logic more but
it will be a bigger change. If you want I can remove the
```exit_status_from_exception``` method from this PR

lib/simplecov.rb

@@ -1,5 +1,7 @@
 # frozen_string_literal: true
 
+require "English"
+
 #
 # Code coverage for ruby 1.9. Please check out README for a full introduction.
 #
@@ -22,6 +24,7 @@ module SimpleCov
   class << self
     attr_accessor :running
     attr_accessor :pid
+    attr_reader :exit_exception
 
     #
     # Sets up SimpleCov to run against your project.
@@ -165,6 +168,27 @@ def usable?
     def clear_result
       @result = nil
     end
+
+    #
+    # Capture the current exception if it exists
+    # This will get called inside the at_exit block
+    #
+    def set_exit_exception
+      @exit_exception = $ERROR_INFO
+    end
+
+    #
+    # Returns the exit status from the exit exception
+    #
+    def exit_status_from_exception
+      return SimpleCov::ExitCodes::SUCCESS unless exit_exception
+
+      if exit_exception.is_a?(SystemExit)
+        exit_exception.status
+      else
+        SimpleCov::ExitCodes::EXCEPTION
+      end
+    end
   end
 end
 

lib/simplecov/defaults.rb

@@ -23,16 +23,9 @@
   # If we are in a different process than called start, don't interfere.
   next if SimpleCov.pid != Process.pid
 
-  @exit_status = if $! # was an exception thrown?
-                   # if it was a SystemExit, use the accompanying status
-                   # otherwise set a non-zero status representing termination by
-                   # some other exception (see github issue 41)
-                   $!.is_a?(SystemExit) ? $!.status : SimpleCov::ExitCodes::EXCEPTION
-                 else
-                   # Store the exit status of the test run since it goes away
-                   # after calling the at_exit proc...
-                   SimpleCov::ExitCodes::SUCCESS
-                 end
+  SimpleCov.set_exit_exception
+
+  @exit_status = SimpleCov.exit_status_from_exception
 
   SimpleCov.at_exit.call
 

spec/simplecov_spec.rb

@@ -107,5 +107,89 @@
         end
       end
     end
+
+    describe ".set_exit_exception" do
+      context "when an exception has occurred" do
+        let(:error) { StandardError.new "SomeError" }
+
+        after do
+          # Clear the exit_exception
+          SimpleCov.set_exit_exception
+        end
+
+        it "captures the current exception" do
+          begin
+            raise error
+          rescue
+            SimpleCov.set_exit_exception
+            expect(SimpleCov.exit_exception).to be(error)
+          end
+        end
+      end
+
+      context "when an exception has not occurred" do
+        it "does set the exit_exception" do
+          SimpleCov.set_exit_exception
+          expect(SimpleCov.exit_exception).to eq(nil)
+        end
+      end
+    end
+
+    describe ".exit_exception" do
+      let(:error) { StandardError.new "SomeError" }
+
+      before do
+        begin
+          raise error
+        rescue
+          SimpleCov.set_exit_exception
+        end
+      end
+
+      after do
+        # Clear the exit_exception
+        SimpleCov.set_exit_exception
+      end
+
+      it "returns the exit exception" do
+        expect(SimpleCov.exit_exception).to be(error)
+      end
+    end
+
+    describe ".exit_status_from_exception" do
+      context "when no exception has occurred" do
+        before do
+          allow(SimpleCov).to receive(:exit_exception).and_return(nil)
+        end
+
+        it "returns SimpleCov::ExitCodes::SUCCESS" do
+          expect(SimpleCov.exit_status_from_exception).to eq(SimpleCov::ExitCodes::SUCCESS)
+        end
+      end
+
+      context "when a SystemExit has occurred" do
+        let(:system_exit) { SystemExit.new(1) }
+
+        before do
+          allow(SimpleCov).to receive(:exit_exception).and_return(system_exit)
+        end
+
+        it "returns the SystemExit status" do
+          expect(SimpleCov.exit_status_from_exception).to eq(system_exit.status)
+        end
+      end
+
+      context "when a non SystemExit occurrs" do
+        let(:error) { StandardError.new "NonSystemExit" }
+
+        before do
+          allow(SimpleCov).to receive(:exit_exception).and_return(error)
+        end
+
+        it "return SimpleCov::ExitCodes::EXCEPTION" do
+          expect(SimpleCov.exit_status_from_exception).to eq(SimpleCov::ExitCodes::EXCEPTION)
+        end
+      end
+    end
   end
 end