Create minitest file to underscored path in "bundle gem" command

...with dashed gem name

In "bundle gem" command with dashed name gem (e.g. foo-bar) generates
`test/test_foo/bar.rb`, but this file contains undefined class `TestFoo`
and moreover, does not include in "bundle exec rake test" target.

Therefore, intentially the first test after gem created is fail, but in
case of gem name contains dash character is not.

The change doings...
(when "bundle gem foo-bar" called)

* create `test/test_foo_bar.rb`
* define `TestFooBar` class in `test/test_foo_bar.rb`

bundler/lib/bundler/cli/gem.rb

@@ -106,7 +106,7 @@ def run
         when "minitest"
           templates.merge!(
             "test/minitest/test_helper.rb.tt" => "test/test_helper.rb",
-            "test/minitest/test_newgem.rb.tt" => "test/test_#{namespaced_path}.rb"
+            "test/minitest/test_newgem.rb.tt" => "test/test_#{underscored_name}.rb"
           )
           config[:test_task] = :test
         when "test-unit"

bundler/lib/bundler/templates/newgem/test/minitest/test_newgem.rb.tt

@@ -2,7 +2,7 @@
 
 require "test_helper"
 
-class Test<%= config[:constant_name] %> < Minitest::Test
+class Test<%= config[:constant_name].gsub('::', '') %> < Minitest::Test
   def test_that_it_has_a_version_number
     refute_nil ::<%= config[:constant_name] %>::VERSION
   end

bundler/spec/commands/newgem_spec.rb

@@ -696,18 +696,22 @@ def create_temporary_dir(dir)
     end
 
     context "gem.test setting set to rspec and --test is set to minitest" do
+      let(:underscored_require_path) { require_path.tr("/", "_") }
+
       before do
         bundle "config set gem.test rspec"
         bundle "gem #{gem_name} --test=minitest"
       end
 
       it "builds spec skeleton" do
-        expect(bundled_app("#{gem_name}/test/test_#{require_path}.rb")).to exist
+        expect(bundled_app("#{gem_name}/test/test_#{underscored_require_path}.rb")).to exist
         expect(bundled_app("#{gem_name}/test/test_helper.rb")).to exist
       end
     end
 
     context "--test parameter set to minitest" do
+      let(:underscored_require_path) { require_path.tr("/", "_") }
+
       before do
         bundle "gem #{gem_name} --test=minitest"
       end
@@ -722,7 +726,7 @@ def create_temporary_dir(dir)
       end
 
       it "builds spec skeleton" do
-        expect(bundled_app("#{gem_name}/test/test_#{require_path}.rb")).to exist
+        expect(bundled_app("#{gem_name}/test/test_#{underscored_require_path}.rb")).to exist
         expect(bundled_app("#{gem_name}/test/test_helper.rb")).to exist
       end
 
@@ -731,11 +735,11 @@ def create_temporary_dir(dir)
       end
 
       it "requires 'test_helper'" do
-        expect(bundled_app("#{gem_name}/test/test_#{require_path}.rb").read).to include(%(require "test_helper"))
+        expect(bundled_app("#{gem_name}/test/test_#{underscored_require_path}.rb").read).to include(%(require "test_helper"))
       end
 
       it "creates a default test which fails" do
-        expect(bundled_app("#{gem_name}/test/test_#{require_path}.rb").read).to include("assert false")
+        expect(bundled_app("#{gem_name}/test/test_#{underscored_require_path}.rb").read).to include("assert false")
       end
     end