ParserFile: use a File instead of a filename

- spec: can use StringIOs instead of loose files

spec/files/github_changelog_params_327

@@ -1,2 +0,0 @@
-exclude-labels=73a91042-da6f-11e5-9335-1040f38d7f90,7adf83b4-da6f-11e5-ae18-1040f38d7f90
-header_label=# My changelog

spec/files/github_changelog_params_incorrect

@@ -1,2 +0,0 @@
-unreleased_label: staging
-unreleased: false

spec/files/github_changelog_params_override

@@ -1,3 +0,0 @@
-unreleased_label=staging
-unreleased=false
-header==== Changelog ===

spec/unit/parse_file_spec.rb

@@ -8,8 +8,8 @@ describe GitHubChangelogGenerator::ParserFile do
     end
 
     context "when file is empty" do
-      let(:options) { { params_file: "spec/files/github_changelog_params_empty" } }
-      let(:parse) { GitHubChangelogGenerator::ParserFile.new(options) }
+      let(:options) { {} }
+      let(:parse) { GitHubChangelogGenerator::ParserFile.new(options, StringIO.new("")) }
 
       it "does not change the options" do
         expect { parse.parse! }.to_not change { options }
@@ -17,17 +17,21 @@ describe GitHubChangelogGenerator::ParserFile do
     end
 
     context "when file is incorrect" do
-      let(:options) { { params_file: "spec/files/github_changelog_params_incorrect" } }
+      let(:options) { {} }
       let(:options_before_change) { options.dup }
-      let(:parse) { GitHubChangelogGenerator::ParserFile.new(options) }
+      let(:file) { StringIO.new("unreleased_label: staging\nunreleased: false") }
+      let(:parse) do
+        GitHubChangelogGenerator::ParserFile.new(options, file)
+      end
       it { expect { parse.parse! }.to raise_error(GitHubChangelogGenerator::ParserError) }
     end
 
     context "when override default values" do
       let(:default_options) { GitHubChangelogGenerator::Parser.default_options }
-      let(:options) { { params_file: "spec/files/github_changelog_params_override" }.merge(default_options) }
+      let(:options) { {}.merge(default_options) }
       let(:options_before_change) { options.dup }
-      let(:parse) { GitHubChangelogGenerator::ParserFile.new(options) }
+      let(:file) { StringIO.new("unreleased_label=staging\nunreleased=false\nheader==== Changelog ===") }
+      let(:parse) { GitHubChangelogGenerator::ParserFile.new(options, file) }
 
       it "changes the options" do
         expect { parse.parse! }.to change { options }
@@ -38,21 +42,22 @@ describe GitHubChangelogGenerator::ParserFile do
       end
 
       context "turns exclude-labels into an Array", bug: '#327' do
-        let(:options) do
-          {
-            params_file: "spec/files/github_changelog_params_327"
-          }
+        let(:file) do
+          StringIO.new(<<EOF
+exclude-labels=73a91042-da6f-11e5-9335-1040f38d7f90,7adf83b4-da6f-11e5-ae18-1040f38d7f90
+header_label=# My changelog
+EOF
+                      )
         end
-
         it "reads exclude_labels into an Array" do
           expect { parse.parse! }.to change { options[:exclude_labels] }
-            .from(nil)
+            .from(default_options[:exclude_labels])
             .to(["73a91042-da6f-11e5-9335-1040f38d7f90", "7adf83b4-da6f-11e5-ae18-1040f38d7f90"])
         end
 
         it "translates given header_label into the :header option" do
           expect { parse.parse! }.to change { options[:header] }
-            .from(nil)
+            .from(default_options[:header])
             .to("# My changelog")
         end
       end