add simple grammar rules and tests for simple cases

grammar.y

@@ -1,8 +1,17 @@
 class Query
     rule
-        expression:
+        target: expression
+                | /* none */ { result = 0 }
+
+          expression: TERM_WITHOUT_QUOTES                                       { result = {:DEFAULT_COLUMN => val[0]} }
+          |     TERM_WITH_QUOTES                                                { result = {:DEFAULT_COLUMN => val[0]} }
+          |     TERM_WITHOUT_QUOTES COLON TERM_WITHOUT_QUOTES                   { result = {val[0] => val[2]} }
+          |     TERM_WITHOUT_QUOTES COLON TERM_WITH_QUOTES                      { result = {val[0] => val[2]} }
 end
 
+---- header
+  require_relative 'lexer'
+
 ---- inner
   def parse(input)
     scan_str(input)

spec/query_parser_spec.rb

@@ -5,5 +5,31 @@ class QueryParserTester
     before do
       @evaluator = Query.new
     end
+
+    it 'tests query with only one search term without quotes and without column name' do
+      @result = @evaluator.parse('-123')
+
+      expect(@result[:DEFAULT_COLUMN]).to eq '-123'
+    end
+
+    it 'tests query with only one search term with quotes and without column name' do
+      @result = @evaluator.parse('"OR 128"')
+
+      expect(@result[:DEFAULT_COLUMN]).to eq '"OR 128"'
+    end
+
+    it 'tests query with one column and search term without quotes' do
+      @result = @evaluator.parse('tag:mta')
+
+      expect(@result['tag']).to eq 'mta'
+    end
+
+    it 'tests query with one column and search term with quotes' do
+      @result = @evaluator.parse('tag:"tag 120"')
+
+      expect(@result['tag']).to eq '"tag 120"'
+    end
+
+
   end
 end