diff --git a/spec/lib/regexp_preview/single_line_spec.rb b/spec/lib/regexp_preview/single_line_spec.rb
new file mode 100644
index 0000000..99d263e
--- /dev/null
+++ b/spec/lib/regexp_preview/single_line_spec.rb
@@ -0,0 +1,183 @@
+require 'spec_helper'
+
+describe RegexpPreview::SingleLine do
+  describe ".initialize" do
+    subject { RegexpPreview::SingleLine.new("log_file.log", format, params) }
+
+    describe "format" do
+      let :params do
+        {
+          regexp: "(?<regexp>regexp)",
+          time_format: "time_format",
+        }
+      end
+
+      shared_examples "should set regexp and time_format from selected format" do
+        it do
+          expect(subject.regexp).to eq regexp
+          expect(subject.time_format).to eq time_format
+          expect(subject.params).to eq params
+        end
+      end
+
+      shared_examples "should set params only" do
+        include_examples "should set regexp and time_format from selected format" do
+          let(:regexp) { nil }
+          let(:time_format) { nil }
+        end
+      end
+
+      context "regexp" do
+        let(:format) { "regexp" }
+
+        it 'should set regexp from params' do
+          expect(subject.regexp).to eq /#{params[:regexp]}/
+          expect(subject.time_format).to be_nil
+          expect(subject.params).to eq params
+        end
+      end
+
+      context "ltsv" do
+        let(:format) { "ltsv" }
+
+        include_examples "should set params only"
+      end
+
+      context "json" do
+        let(:format) { "json" }
+
+        include_examples "should set params only"
+      end
+
+      context "csv" do
+        let(:format) { "csv" }
+
+        include_examples "should set params only"
+      end
+
+      context "tsv" do
+        let(:format) { "tsv" }
+
+        include_examples "should set params only"
+      end
+
+      context "syslog" do # "apache", "nginx", etc
+        let(:format) { "syslog" }
+
+        include_examples "should set regexp and time_format from selected format" do
+          let(:regexp) do
+            /^(?<time>[^ ]*\s*[^ ]* [^ ]*) (?<host>[^ ]*) (?<ident>[a-zA-Z0-9_\/\.\-]*)(?:\[(?<pid>[0-9]+)\])?(?:[^\:]*\:)? *(?<message>.*)$/
+          end
+          let(:time_format) { "%b %d %H:%M:%S" }
+        end
+      end
+
+      context "apache" do
+        let(:format) { "apache" }
+
+        include_examples "should set regexp and time_format from selected format" do
+          let(:regexp) do
+            /^(?<host>[^ ]*) [^ ]* (?<user>[^ ]*) \[(?<time>[^\]]*)\] "(?<method>\S+)(?: +(?<path>[^ ]*) +\S*)?" (?<code>[^ ]*) (?<size>[^ ]*)(?: "(?<referer>[^\"]*)" "(?<agent>[^\"]*)")?$/
+          end
+          let(:time_format) { "%d/%b/%Y:%H:%M:%S %z" }
+        end
+      end
+
+      context "nginx" do
+        let(:format) { "nginx" }
+
+        include_examples "should set regexp and time_format from selected format" do
+          let(:regexp) do
+            /^(?<remote>[^ ]*) (?<host>[^ ]*) (?<user>[^ ]*) \[(?<time>[^\]]*)\] "(?<method>\S+)(?: +(?<path>[^\"]*?)(?: +\S*)?)?" (?<code>[^ ]*) (?<size>[^ ]*)(?: "(?<referer>[^\"]*)" "(?<agent>[^\"]*)")?$/
+          end
+          let(:time_format) { "%d/%b/%Y:%H:%M:%S %z" }
+        end
+      end
+    end
+  end
+
+  describe "#matches_json" do
+    let(:logfile) { File.expand_path(logfile_path, Rails.root) }
+    let :params do
+      {
+        regexp: "(?<regexp>bar)", # bar from error0.log
+        time_format: "time_format",
+      }
+    end
+
+    subject { RegexpPreview::SingleLine.new(logfile, format, params).matches_json }
+
+    describe "format" do
+      context "regexp" do
+        let(:format) { "regexp" }
+        let(:logfile_path) { "./spec/support/fixtures/error0.log" }
+
+        it 'should have regexp only in [:params][:setting]' do
+          setting_json = {
+            regexp: params[:regexp],
+            time_format: nil
+          }
+
+          expect(subject[:params][:setting]).to eq setting_json
+        end
+
+        it 'should include matches info' do
+          matches_info = {
+            whole: "bar",
+            matches: [
+              { key: "regexp", matched: "bar", pos: [0, 3] }
+            ]
+          }
+          expect(subject[:matches]).to include matches_info
+        end
+      end
+
+      context "csv" do
+        let(:format) { "csv" }
+        let(:logfile_path) { "./spec/support/fixtures/error0.log" }
+
+        it 'should not have regexp and time_format in [:params][:setting]' do
+          setting_json = {
+            regexp: nil,
+            time_format: nil
+          }
+
+          expect(subject[:params][:setting]).to eq setting_json
+        end
+
+        it 'should not have matches_info' do
+          expect(subject[:matches]).to be_empty
+        end
+      end
+
+      context "syslog" do
+        let(:format) { "syslog" }
+        let(:logfile_path) { "./spec/support/fixtures/error4.log" }
+
+        it 'should set regexp and time_format from syslog format' do
+          setting_json = {
+            regexp: "^(?<time>[^ ]*\\s*[^ ]* [^ ]*) (?<host>[^ ]*) (?<ident>[a-zA-Z0-9_/\\.\\-]*)(?:\\[(?<pid>[0-9]+)\\])?(?:[^\\:]*\\:)? *(?<message>.*)$",
+            time_format: "%b %d %H:%M:%S",
+          }
+
+          expect(subject[:params][:setting]).to eq setting_json
+        end
+
+        it 'should include matches info' do
+          matches_info = {
+            whole: "2014-05-27 10:54:37 +0900 [info]: listening fluent socket on 0.0.0.0:24224",
+            matches: [
+              { key: "time", matched: "2014-05-27 10:54:37 +0900", pos: [0, 25] },
+              { key: "host", matched: "[info]:", pos: [26, 33] },
+              { key: "ident", matched: "listening", pos: [34, 43] },
+              { key: "pid", matched: nil, pos: [nil, nil] },
+              { key: "message", matched: "24224", pos: [69, 74] }
+            ]
+          }
+
+          expect(subject[:matches]).to include matches_info
+        end
+      end
+    end
+  end
+end
diff --git a/spec/support/fixtures/error4.log b/spec/support/fixtures/error4.log
new file mode 100644
index 0000000..a427df3
--- /dev/null
+++ b/spec/support/fixtures/error4.log
@@ -0,0 +1 @@
+2014-05-27 10:54:37 +0900 [info]: listening fluent socket on 0.0.0.0:24224