Merge branch 'master' into java_alternative_without_dependencies

Author: izuzak

.travis.yml

@@ -3,10 +3,10 @@ language: ruby
 cache: bundler
 script: script/test
 rvm:
-  - 2.3.8
-  - 2.4.5
-  - 2.5.3
-  - 2.6.1
+  - 2.6.7
+  - 2.7.3
+  - 3.0.1
+  - truffleruby-head
 before_install: gem install bundler
 addons:
  apt:

README.md

@@ -24,7 +24,7 @@ Wrap a `use` block around the code's original behavior, and wrap `try` around th
 
 * It decides whether or not to run the `try` block,
 * Randomizes the order in which `use` and `try` blocks are run,
-* Measures the durations of all behaviors,
+* Measures the durations of all behaviors in seconds,
 * Compares the result of `try` to the result of `use`,
 * Swallow and record exceptions raised in the `try` block when overriding `raised`, and
 * Publishes all this information.
@@ -62,7 +62,7 @@ class MyExperiment
 
   attr_accessor :name
 
-  def initialize(name:)
+  def initialize(name)
     @name = name
   end
 
@@ -82,15 +82,10 @@ class MyExperiment
     p result
   end
 end
-
-# replace `Scientist::Default` as the default implementation
-module Scientist::Experiment
-  def self.new(name)
-    MyExperiment.new(name: name)
-  end
-end
 ```
 
+When `Scientist::Experiment` is included in a class, it automatically sets it as the default implementation via `Scientist::Experiment.set_default`. This `set_default` call is is skipped if you include `Scientist::Experiment` in a module.
+
 Now calls to the `science` helper will load instances of `MyExperiment`.
 
 ### Controlling comparison
@@ -114,6 +109,38 @@ class MyWidget
 end
 ```
 
+If either the control block or candidate block raises an error, Scientist compares the two observations' classes and messages using `==`. To override this behavior, use `compare_error` to define how to compare observed errors instead:
+
+```ruby
+class MyWidget
+  include Scientist
+
+  def slug_from_login(login)
+    science "slug_from_login" do |e|
+      e.use { User.slug_from_login login }         # returns String instance or ArgumentError
+      e.try { UserService.slug_from_login login }  # returns String instance or ArgumentError
+
+      compare_error_message_and_class = -> (control, candidate) do
+        control.class == candidate.class && 
+        control.message == candidate.message
+      end
+
+      compare_argument_errors = -> (control, candidate) do
+        control.class == ArgumentError &&
+        candidate.class == ArgumentError &&
+        control.message.start_with?("Input has invalid characters") &&
+        candidate.message.star_with?("Invalid characters in input") 
+      end
+
+      e.compare_error do |control, candidate|
+        compare_error_message_and_class.call(control, candidate) ||
+        compare_argument_errors.call(control, candidate)
+      end
+    end
+  end
+end
+```
+
 ### Adding context
 
 Results aren't very useful without some way to identify them. Use the `context` method to add to or retrieve the context for an experiment:
@@ -233,7 +260,7 @@ def admin?(user)
 end
 ```
 
-The ignore blocks are only called if the *values* don't match. If one observation raises an exception and the other doesn't, it's always considered a mismatch. If both observations raise different exceptions, that is also considered a mismatch.
+The ignore blocks are only called if the *values* don't match. Unless a `compare_error` comparator is defined, two cases are considered mismatches: a) one observation raising an exception and the other not, b) observations raising exceptions with different classes or messages.
 
 ### Enabling/disabling experiments
 
@@ -262,7 +289,7 @@ class MyExperiment
 
   attr_accessor :name, :percent_enabled
 
-  def initialize(name:)
+  def initialize(name)
     @name = name
     @percent_enabled = 100
   end
@@ -400,6 +427,8 @@ Scientist rescues and tracks _all_ exceptions raised in a `try` or `use` block,
 Scientist::Observation::RESCUES.replace [StandardError]
 ```
 
+**Timeout ⏲️**: If you're introducing a candidate that could possibly timeout, use caution. ⚠️ While Scientist rescues all exceptions that occur in the candidate block, it *does not* protect you from timeouts, as doing so would be complicated. It would likely require running the candidate code in a background job and tracking the time of a request. We feel the cost of this complexity would outweigh the benefit, so make sure that your code doesn't cause timeouts. This risk can be reduced by running the experiment on a low percentage so that users can (most likely) bypass the experiment by refreshing the page if they hit a timeout. See [Ramping up experiments](#ramping-up-experiments) below for how details on how to set the percentage for your experiment.
+
 #### In a Scientist callback
 
 If an exception is raised within any of Scientist's internal helpers, like `publish`, `compare`, or `clean`, the `raised` method is called with the symbol name of the internal operation that failed and the exception that was raised. The default behavior of `Scientist::Default` is to simply re-raise the exception. Since this halts the experiment entirely, it's often a better idea to handle this error and continue so the experiment as a whole isn't canceled entirely:
@@ -544,6 +573,7 @@ Be on a Unixy box. Make sure a modern Bundler is available. `script/test` runs t
 - [trello/scientist](https://github.com/trello/scientist) (node.js)
 - [ziyasal/scientist.js](https://github.com/ziyasal/scientist.js) (node.js, ES6)
 - [TrueWill/tzientist](https://github.com/TrueWill/tzientist) (node.js, TypeScript)
+- [TrueWill/paleontologist](https://github.com/TrueWill/paleontologist) (Deno, TypeScript)
 - [yeller/laboratory](https://github.com/yeller/laboratory) (Clojure)
 - [lancew/Scientist](https://github.com/lancew/Scientist) (Perl 5)
 - [lancew/ScientistP6](https://github.com/lancew/ScientistP6) (Perl 6)
@@ -554,7 +584,8 @@ Be on a Unixy box. Make sure a modern Bundler is available. `script/test` runs t
 - [spoptchev/scientist](https://github.com/spoptchev/scientist) (Kotlin / Java)
 - [junkpiano/scientist](https://github.com/junkpiano/scientist) (Swift)
 - [serverless scientist](http://serverlessscientist.com/) (AWS Lambda)
-- [Mister Spex Scientist](https://github.com/MisterSpex/misterspex-scientist/) (Java, no dependencies)
+- [fightmegg/scientist](https://github.com/fightmegg/scientist) (TypeScript, Browser / Node.js)
+- [MisterSpex/misterspex-scientist](https://github.com/MisterSpex/misterspex-scientist) (Java, no dependencies)
 
 ## Maintainers
 

lib/scientist/experiment.rb

@@ -9,12 +9,22 @@ module Scientist::Experiment
   # If this is nil, raise_on_mismatches class attribute is used instead.
   attr_accessor :raise_on_mismatches
 
-  # Create a new instance of a class that implements the Scientist::Experiment
-  # interface.
-  #
-  # Override this method directly to change the default implementation.
+  def self.included(base)
+    self.set_default(base) if base.instance_of?(Class)
+    base.extend RaiseOnMismatch
+  end
+
+  # Instantiate a new experiment (using the class given to the .set_default method).
   def self.new(name)
-    Scientist::Default.new(name)
+    (@experiment_klass || Scientist::Default).new(name)
+  end
+
+  # Configure Scientist to use the given class for all future experiments
+  # (must implement the Scientist::Experiment interface).
+  #
+  # Called automatically when new experiments are defined.
+  def self.set_default(klass)
+    @experiment_klass = klass
   end
 
   # A mismatch, raised when raise_on_mismatches is enabled.
@@ -67,10 +77,6 @@ def raise_on_mismatches?
     end
   end
 
-  def self.included(base)
-    base.extend RaiseOnMismatch
-  end
-
   # Define a block of code to run before an experiment begins, if the experiment
   # is enabled.
   #
@@ -128,6 +134,16 @@ def compare(*args, &block)
     @_scientist_comparator = block
   end
 
+  # A block which compares two experimental errors.
+  #
+  # The block must take two arguments, the control Error and a candidate Error,
+  # and return true or false.
+  #
+  # Returns the block.
+  def compare_errors(*args, &block)
+    @_scientist_error_comparator = block
+  end
+
   # A Symbol-keyed Hash of extra experiment data.
   def context(context = nil)
     @_scientist_context ||= {}
@@ -171,13 +187,9 @@ def name
     "experiment"
   end
 
-  # Internal: compare two observations, using the configured compare block if present.
+  # Internal: compare two observations, using the configured compare and compare_errors lambdas if present.
   def observations_are_equivalent?(a, b)
-    if @_scientist_comparator
-      a.equivalent_to?(b, &@_scientist_comparator)
-    else
-      a.equivalent_to? b
-    end
+    a.equivalent_to? b, @_scientist_comparator, @_scientist_error_comparator
   rescue StandardError => ex
     raised :compare, ex
     false
@@ -216,17 +228,7 @@ def run(name = nil)
       @_scientist_before_run.call
     end
 
-    observations = []
-
-    behaviors.keys.shuffle.each do |key|
-      block = behaviors[key]
-      fabricated_duration = @_scientist_fabricated_durations && @_scientist_fabricated_durations[key]
-      observations << Scientist::Observation.new(key, self, fabricated_duration: fabricated_duration, &block)
-    end
-
-    control = observations.detect { |o| o.name == name }
-
-    result = Scientist::Result.new self, observations, control
+    result = generate_result(name)
 
     begin
       publish(result)
@@ -242,11 +244,9 @@ def run(name = nil)
       end
     end
 
-    if control.raised?
-      raise control.exception
-    else
-      control.value
-    end
+    control = result.control
+    raise control.exception if control.raised?
+    control.value
   end
 
   # Define a block that determines whether or not the experiment should run.
@@ -304,4 +304,18 @@ def raise_on_mismatches?
   def fabricate_durations_for_testing_purposes(fabricated_durations = {})
     @_scientist_fabricated_durations = fabricated_durations
   end
+
+  # Internal: Generate the observations and create the result from those and the control.
+  def generate_result(name)
+    observations = []
+
+    behaviors.keys.shuffle.each do |key|
+      block = behaviors[key]
+      fabricated_duration = @_scientist_fabricated_durations && @_scientist_fabricated_durations[key]
+      observations << Scientist::Observation.new(key, self, fabricated_duration: fabricated_duration, &block)
+    end
+
+    control = observations.detect { |o| o.name == name }
+    Scientist::Result.new(self, observations, control)
+  end
 end

lib/scientist/observation.rb

@@ -8,9 +8,6 @@ class Scientist::Observation
   # The experiment this observation is for
   attr_reader :experiment
 
-  # The instant observation began.
-  attr_reader :now
-
   # The String name of the behavior.
   attr_reader :name
 
@@ -26,7 +23,6 @@ class Scientist::Observation
   def initialize(name, experiment, fabricated_duration: nil, &block)
     @name       = name
     @experiment = experiment
-    @now        = Time.now
 
     starting = Process.clock_gettime(Process::CLOCK_MONOTONIC, :float_second) unless fabricated_duration
     begin
@@ -49,25 +45,34 @@ def cleaned_value
 
   # Is this observation equivalent to another?
   #
-  # other      - the other Observation in question
-  # comparator - an optional comparison block. This observation's value and the
-  #              other observation's value are yielded to this to determine
-  #              their equivalency. Block should return true/false.
+  # other            - the other Observation in question
+  # comparator       - an optional comparison proc. This observation's value and the
+  #                    other observation's value are passed to this to determine
+  #                    their equivalency. Proc should return true/false.
+  # error_comparator - an optional comparison proc. This observation's Error and the
+  #                    other observation's Error are passed to this to determine
+  #                    their equivalency. Proc should return true/false.
   #
   # Returns true if:
   #
   # * The values of the observation are equal (using `==`)
   # * The values of the observations are equal according to a comparison
-  #   block, if given
+  #   proc, if given
+  # * The exceptions raised by the obeservations are equal according to the
+  #   error comparison proc, if given.
   # * Both observations raised an exception with the same class and message.
   #
   # Returns false otherwise.
-  def equivalent_to?(other, &comparator)
+  def equivalent_to?(other, comparator=nil, error_comparator=nil)
     return false unless other.is_a?(Scientist::Observation)
 
     if raised? || other.raised?
-      return other.exception.class == exception.class &&
-        other.exception.message == exception.message
+      if error_comparator
+        return error_comparator.call(exception, other.exception)
+      else
+        return other.exception.class == exception.class &&
+          other.exception.message == exception.message
+      end
     end
 
     if comparator

lib/scientist/version.rb

@@ -1,3 +1,3 @@
 module Scientist
-  VERSION = "1.4.0"
+  VERSION = "1.6.0"
 end

test/scientist/experiment_test.rb

@@ -2,6 +2,9 @@
   class Fake
     include Scientist::Experiment
 
+    # Undo auto-config magic / preserve default behavior of Scientist::Experiment.new
+    Scientist::Experiment.set_default(nil)
+
     def initialize(*args)
     end
 
@@ -28,6 +31,24 @@ def publish(result)
     @ex = Fake.new
   end
 
+  it "sets the default on inclusion" do
+    klass = Class.new do
+      include Scientist::Experiment
+
+      def initialize(name)
+      end
+    end
+
+    assert_kind_of klass, Scientist::Experiment.new("hello")
+
+    Scientist::Experiment.set_default(nil)
+  end
+
+  it "doesn't set the default on inclusion when it's a module" do
+    Module.new { include Scientist::Experiment }
+    assert_kind_of Scientist::Default, Scientist::Experiment.new("hello")
+  end
+
   it "has a default implementation" do
     ex = Scientist::Experiment.new("hello")
     assert_kind_of Scientist::Default, ex
@@ -180,6 +201,18 @@ def @ex.publish(result)
     assert @ex.published_result.matched?
   end
 
+  it "compares errors with an error comparator block if provided" do
+    @ex.compare_errors { |a, b| a.class == b.class }
+    @ex.use { raise "foo" }
+    @ex.try { raise "bar" }
+
+    resulting_error = assert_raises RuntimeError do
+      @ex.run
+    end
+    assert_equal "foo", resulting_error.message
+    assert @ex.published_result.matched?
+  end
+
   it "knows how to compare two experiments" do
     a = Scientist::Observation.new(@ex, "a") { 1 }
     b = Scientist::Observation.new(@ex, "b") { 2 }
@@ -546,7 +579,7 @@ def @ex.raised(op, exception)
         assert_equal "  \"value\"", lines[2]
         assert_equal "candidate:", lines[3]
         assert_equal "  #<RuntimeError: error>", lines[4]
-        assert_match %r(    test/scientist/experiment_test.rb:\d+:in `block), lines[5]
+        assert_match %r(test/scientist/experiment_test.rb:\d+:in `block), lines[5]
       end
     end
   end