Add minitest assert_perform_linear_number_of_queries

CHANGELOG.md

@@ -1,7 +1,7 @@
 ## master (unreleased)
 
 - Fix table stats summary when queries use backticks to surround table names ([@andrewhampton])
-- Add rspec matcher for linear query. ([@caalberts][])
+- Add support to test for linear query. ([@caalberts][])
 
 ## 0.5.0 (2020-09-07)
 

README.md

@@ -147,6 +147,18 @@ def test_no_n_plus_one_error
 end
 ```
 
+You can also use `assert_perform_linear_number_of_queries` to test for linear queries:
+
+```ruby
+def test_no_n_plus_one_error
+  populate = ->(n) { create_list(:post, n) }
+
+  assert_perform_linear_number_of_queries(slope: 1, populate: populate) do
+    Post.find_each { |p| p.user.name }
+  end
+end
+```
+
 You can also specify custom scale factors or filter patterns:
 
 ```ruby

lib/n_plus_one_control/minitest.rb

@@ -29,6 +29,29 @@ def assert_perform_constant_number_of_queries(
       assert counts.max == counts.min, NPlusOneControl.failure_message(:constant_queries, queries)
     end
 
+    def assert_perform_linear_number_of_queries(
+      slope: 1,
+      populate: nil,
+      matching: nil,
+      scale_factors: nil,
+      warmup: nil
+    )
+
+      raise ArgumentError, "Block is required" unless block_given?
+
+      warming_up warmup
+
+      @executor = NPlusOneControl::Executor.new(
+        population: populate || population_method,
+        matching: matching || NPlusOneControl.default_matching,
+        scale_factors: scale_factors || NPlusOneControl.default_scale_factors
+      )
+
+      queries = @executor.call { yield }
+
+      assert linear?(queries, slope: slope), NPlusOneControl.failure_message(:linear_queries, queries)
+    end
+
     def current_scale
       @executor&.current_scale
     end
@@ -42,6 +65,16 @@ def warming_up(warmup)
     def population_method
       methods.include?(:populate) ? method(:populate) : nil
     end
+
+    def linear?(queries, slope:)
+      queries.each_cons(2).all? do |pair|
+        scales = pair.map(&:first)
+        query_lists = pair.map(&:last)
+
+        actual_slope = (query_lists[1].size - query_lists[0].size) / (scales[1] - scales[0])
+        actual_slope <= slope
+      end
+    end
   end
 end
 

tests/minitest_test.rb

@@ -2,7 +2,7 @@
 
 require_relative "test_helper"
 
-class TestMinitest < Minitest::Test
+class TestMinitestConstantQueries < Minitest::Test
   def test_no_n_plus_one_error
     populate = ->(n) { create_list(:post, n) }
 
@@ -48,6 +48,60 @@ def test_no_n_plus_one_error_with_matching
   end
 end
 
+class TestMinitestLinearQueries < Minitest::Test
+  def test_constant_queries
+    populate = ->(n) { create_list(:post, n) }
+
+    assert_perform_linear_number_of_queries(slope: 1, populate: populate) do
+      Post.preload(:user).find_each { |p| p.user.name }
+    end
+  end
+
+  def test_no_n_plus_one_error
+    populate = ->(n) { create_list(:post, n) }
+
+    assert_perform_linear_number_of_queries(slope: 1, populate: populate) do
+      Post.find_each { |p| p.user.name }
+    end
+  end
+
+  def test_with_n_plus_one_error
+    populate = ->(n) { create_list(:post, n) }
+
+    e = assert_raises Minitest::Assertion do
+      assert_perform_linear_number_of_queries(slope: 1, populate: populate) do
+        Post.find_each { |p| "#{p.user.name} #{p.category.name}" }
+      end
+    end
+
+    assert_match "Expected to make linear number of queries", e.message
+    assert_match "5 for N=2", e.message
+    assert_match "7 for N=3", e.message
+  end
+
+  def test_no_n_plus_one_error_with_scale_factors
+    populate = ->(n) { create_list(:post, n) }
+
+    assert_perform_linear_number_of_queries(
+      populate: populate,
+      scale_factors: [2, 3]
+    ) do
+      Post.find_each { |p| p.user.name }
+    end
+  end
+
+  def test_no_n_plus_one_error_with_matching
+    populate = ->(n) { create_list(:post, n) }
+
+    assert_perform_linear_number_of_queries(
+      populate: populate,
+      matching: /users/
+    ) do
+      Post.find_each { |p| p.user.name }
+    end
+  end
+end
+
 class TestMinitestPopulateMethod < Minitest::Test
   def populate(n)
     create_list(:post, n)