Add more tests and docs for issue indexer, add db indexer type for searching from database (#6144)

* add more tests and docs for issue indexer, add db indexer type for searching from database

* fix typo

* fix typo

* fix lint

* improve docs

models/issue_test.go

@@ -295,3 +295,28 @@ func TestIssue_loadTotalTimes(t *testing.T) {
 	assert.NoError(t, ms.loadTotalTimes(x))
 	assert.Equal(t, int64(3662), ms.TotalTrackedTime)
 }
+
+func TestIssue_SearchIssueIDsByKeyword(t *testing.T) {
+	assert.NoError(t, PrepareTestDatabase())
+
+	total, ids, err := SearchIssueIDsByKeyword("issue2", 1, 10, 0)
+	assert.NoError(t, err)
+	assert.EqualValues(t, 1, total)
+	assert.EqualValues(t, []int64{2}, ids)
+
+	total, ids, err = SearchIssueIDsByKeyword("first", 1, 10, 0)
+	assert.NoError(t, err)
+	assert.EqualValues(t, 1, total)
+	assert.EqualValues(t, []int64{1}, ids)
+
+	total, ids, err = SearchIssueIDsByKeyword("for", 1, 10, 0)
+	assert.NoError(t, err)
+	assert.EqualValues(t, 4, total)
+	assert.EqualValues(t, []int64{1, 2, 3, 5}, ids)
+
+	// issue1's comment id 2
+	total, ids, err = SearchIssueIDsByKeyword("good", 1, 10, 0)
+	assert.NoError(t, err)
+	assert.EqualValues(t, 1, total)
+	assert.EqualValues(t, []int64{1}, ids)
+}