Drop pre-2.7 Ruby version checks

The gemspec already requires Ruby >= 2.7, so RUBY_VERSION < "2.5"/"2.6"
guards are dead code. Trim the runtime checks in result_adapter_spec.rb
and the @rails6 / @Ruby26 cucumber gates, and condense the historical
Ruby 2.5/2.6 coverage-API commentary in simplecov.rb. The remaining
runtime feature detection (`coverage_start_arguments_supported?`,
TruffleRuby/JRuby engine skips) is preserved — those guard alternate
engines, not Ruby versions.

Author: sferik

features/oneshot_line_coverage.feature

@@ -1,4 +1,4 @@
-@rspec @oneshot_line_coverage @ruby26
+@rspec @oneshot_line_coverage
 Feature:
 
   Simply executing oneshot_line coverage gives ok results.

features/rspec_rails.feature

@@ -1,4 +1,4 @@
-@rspec @disable-bundler @rails6
+@rspec @disable-bundler
 
 Feature:
   Make sure that a fairly standard rspec-rails setup within a rails

features/support/env.rb

@@ -53,16 +53,6 @@ def call(env)
   skip_this_scenario unless SimpleCov.branch_coverage_supported?
 end
 
-Before("@rails6") do
-  # Rails 6 only supports Ruby 2.5+
-  skip_this_scenario if Gem::Version.new(RUBY_VERSION) < Gem::Version.new("2.5")
-end
-
-Before("@ruby26") do
-  # oneshot_lines coverage is supported by Ruby 2.6+
-  skip_this_scenario if Gem::Version.new(RUBY_VERSION) < Gem::Version.new("2.6")
-end
-
 Before("@process_fork") do
   # Process.fork is NotImplementedError in jruby
   skip_this_scenario if jruby?

lib/simplecov.rb

@@ -354,33 +354,9 @@ def initial_setup(profile, &block)
     # With Negative branch it supports only line coverage measurement type
     #
     def start_coverage_measurement
-      # This blog post gives a good run down of the coverage criterias introduced
-      # in Ruby 2.5: https://blog.bigbinary.com/2018/04/11/ruby-2-5-supports-measuring-branch-and-method-coverages.html
-      # There is also a nice writeup of the different coverage criteria made in this
-      # comment  https://github.com/simplecov-ruby/simplecov/pull/692#discussion_r281836176 :
-      # Ruby < 2.5:
-      # https://github.com/ruby/ruby/blob/v1_9_3_374/ext/coverage/coverage.c
-      # traditional mode (Array)
-      #
-      # Ruby 2.5:
-      # https://bugs.ruby-lang.org/issues/13901
-      # https://github.com/ruby/ruby/blob/v2_5_3/ext/coverage/coverage.c
-      # default: traditional/compatible mode (Array)
-      # :lines - like traditional mode but using Hash
-      # :branches
-      # :methods
-      # :all - same as lines + branches + methods
-      #
-      # Ruby >= 2.6:
-      # https://bugs.ruby-lang.org/issues/15022
-      # https://github.com/ruby/ruby/blob/v2_6_3/ext/coverage/coverage.c
-      # default: traditional/compatible mode (Array)
-      # :lines - like traditional mode but using Hash
-      # :branches
-      # :methods
-      # :oneshot_lines - can not be combined with lines
-      # :all - same as lines + branches + methods
-      #
+      # CRuby's `Coverage.start` accepts a criteria hash since 2.5; alternate
+      # engines (older JRuby/TruffleRuby) may still ship the no-arg form, so
+      # fall back when the runtime doesn't accept arguments.
       if coverage_start_arguments_supported?
         start_coverage_with_criteria
       else

lib/simplecov/simulate_coverage.rb

@@ -8,10 +8,9 @@ module SimulateCoverage
   module_function
 
     #
-    # Simulate normal file coverage report on
-    # ruby 2.5 and return similar hash with lines and branches keys
-    #
-    # Happens when a file wasn't required but still tracked.
+    # Simulate a file coverage report for a file that was tracked but never
+    # required. Returns the same hash shape as `Coverage.result` (lines,
+    # branches, methods).
     #
     # @return [Hash]
     #

spec/result_adapter_spec.rb

@@ -10,9 +10,7 @@
 
   describe "with oneshot_lines coverage" do
     before do
-      if Gem::Version.new(RUBY_VERSION) < Gem::Version.new("2.6") || RUBY_ENGINE == "truffleruby"
-        skip "oneshot_lines coverage not supported"
-      end
+      skip "oneshot_lines coverage not supported on truffleruby" if RUBY_ENGINE == "truffleruby"
     end
 
     context "when all tracked files exist" do