Filter stop words when searching posts in mysql (#14509)

store/sqlstore/post_store_test.go

@@ -4,6 +4,7 @@
 package sqlstore
 
 import (
+	"github.com/stretchr/testify/require"
 	"testing"
 
 	"github.com/mattermost/mattermost-server/v5/store/searchtest"
@@ -17,3 +18,47 @@ func TestPostStore(t *testing.T) {
 func TestSearchPostStore(t *testing.T) {
 	StoreTestWithSearchTestEngine(t, searchtest.TestSearchPostStore)
 }
+
+func TestMysqlStopWords(t *testing.T) {
+	mysqlStopWordsTests := []struct {
+		Name     string
+		Args     []string
+		Expected []string
+		Empty    bool
+	}{
+		{
+			Name:     "Should remove only the stop words",
+			Args:     []string{"where is my car", "so this is real", "test this-and-that is awesome"},
+			Expected: []string{"my car", "so real", "test this-and-that awesome"},
+		},
+		{
+			Name:     "Should not remove part of a word containg stop words",
+			Args:     []string{"whereabouts", "wherein", "tothis", "thisorthat", "waswhen", "whowas", "inthe", "whowill", "thewww"},
+			Expected: []string{"whereabouts", "wherein", "tothis", "thisorthat", "waswhen", "whowas", "inthe", "whowill", "thewww"},
+		},
+		{
+			Name:  "Should remove all words from terms",
+			Args:  []string{"where about", "where in", "to this", "this or that", "was when", "who was", "in the", "who will", "the www"},
+			Empty: true,
+		},
+		{
+			Name:     "Should not remove part of a word containg stop words separated by hyphens",
+			Args:     []string{"where-about", "where-in", "to-this", "this-or-that", "was-when", "who-was", "in-the", "who-will", "the-www"},
+			Expected: []string{"where-about", "where-in", "to-this", "this-or-that", "was-when", "who-was", "in-the", "who-will", "the-www"},
+		},
+	}
+
+	for _, tc := range mysqlStopWordsTests {
+		t.Run(tc.Name, func(t *testing.T) {
+			for i, term := range tc.Args {
+				got, err := removeMysqlStopWordsFromTerms(term)
+				require.NoError(t, err)
+				if tc.Empty {
+					require.Empty(t, got)
+				} else {
+					require.Equal(t, tc.Expected[i], got)
+				}
+			}
+		})
+	}
+}