Migrate error_test to RSpec (#1456)

lib/ddtrace/error.rb

@@ -16,6 +16,8 @@ def self.build_from(value)
 
     def initialize(type = nil, message = nil, backtrace = nil)
       backtrace = Array(backtrace).join("\n")
+
+      # DEV: We should measure if `Utils.utf8_encode` is still needed in practice.
       @type = Utils.utf8_encode(type)
       @message = Utils.utf8_encode(message)
       @backtrace = Utils.utf8_encode(backtrace)

spec/ddtrace/error_spec.rb

@@ -0,0 +1,90 @@
+RSpec.describe Datadog::Error do
+  context 'with default values' do
+    let(:error) { described_class.new }
+
+    it do
+      expect(error.type).to be_empty
+      expect(error.message).to be_empty
+      expect(error.backtrace).to be_empty
+    end
+
+    # Empty strings were being interpreted as ASCII strings breaking `msgpack`
+    # decoding on the agent-side.
+    it 'encodes default values in UTF-8' do
+      error = described_class.new
+
+      expect(error.type.encoding).to eq(::Encoding::UTF_8)
+      expect(error.message.encoding).to eq(::Encoding::UTF_8)
+      expect(error.backtrace.encoding).to eq(::Encoding::UTF_8)
+    end
+  end
+
+  context 'with all values provided' do
+    let(:error) { described_class.new('ErrorClass', 'message', %w[line1 line2 line3]) }
+
+    it do
+      expect(error.type).to eq('ErrorClass')
+      expect(error.message).to eq('message')
+      expect(error.backtrace).to eq("line1\nline2\nline3")
+    end
+  end
+
+  describe '.build_from' do
+    subject(:error) { described_class.build_from(value) }
+
+    context 'with an exception' do
+      let(:value) { ZeroDivisionError.new('divided by 0') }
+
+      it do
+        expect(error.type).to eq('ZeroDivisionError')
+        expect(error.message).to eq('divided by 0')
+        expect(error.backtrace).to be_empty
+      end
+    end
+
+    context 'with an array' do
+      let(:value) { ['ZeroDivisionError', 'divided by 0'] }
+
+      it do
+        expect(error.type).to eq('ZeroDivisionError')
+        expect(error.message).to eq('divided by 0')
+        expect(error.backtrace).to be_empty
+      end
+    end
+
+    context 'with a custom object responding to :message' do
+      let(:value) do
+        # RSpec 'double' hijacks the #class method, thus not allowing us
+        # to organically test the `Error#type` inferred for this object.
+        clazz = stub_const('Test::CustomMessage', Struct.new(:message))
+        clazz.new('custom msg')
+      end
+
+      it do
+        expect(error.type).to eq('Test::CustomMessage')
+        expect(error.message).to eq('custom msg')
+        expect(error.backtrace).to be_empty
+      end
+    end
+
+    context 'with nil' do
+      let(:value) { nil }
+
+      it do
+        expect(error.type).to be_empty
+        expect(error.message).to be_empty
+        expect(error.backtrace).to be_empty
+      end
+    end
+
+    context 'with a utf8 incompatible message' do
+      let(:value) { StandardError.new("\xC2".force_encoding(::Encoding::ASCII_8BIT)) }
+
+      it 'discards unencodable value' do
+        expect(error.type).to eq('StandardError')
+        expect(error.message).to be_empty
+        expect(error.backtrace).to be_empty
+      end
+    end
+  end
+end