Always query for a minimum of 20 results from Elasticsearch

Fallback and interpolation queries rely on several results coming back
from Elasticsearch to ensure the best result is returned. It was
possible that queries with `size=1` would not return enough results from
Elasticsearch. This change ensures even with `size=1` a sufficient
number of results are returned.

Fixes https://github.com/pelias/pelias/issues/562

middleware/sizeCalculator.js

@@ -2,6 +2,8 @@ var _ = require('lodash');
 
 var SIZE_PADDING = 2;
 
+var MIN_QUERY_SIZE = 20;
+
 /**
  * Utility for calculating query result size
  * incorporating padding for dedupe process
@@ -24,12 +26,7 @@ function setup() {
  * @returns {number}
  */
 function calculateSize(cleanSize) {
-  switch (cleanSize || 1) {
-    case 1:
-      return 1;
-    default:
-      return cleanSize * SIZE_PADDING;
-  }
+  return Math.max(MIN_QUERY_SIZE, cleanSize * SIZE_PADDING);
 }
 
 module.exports = setup;

test/unit/helper/sizeCalculator.js

@@ -25,7 +25,7 @@ module.exports.tests.valid = function(test, common) {
   test('size=0', function (t) {
     setup(0);
     calcSize(req, {}, function () {
-      t.equal(req.clean.querySize, 1);
+      t.equal(req.clean.querySize, 20);
       t.end();
     });
   });
@@ -33,7 +33,7 @@ module.exports.tests.valid = function(test, common) {
   test('size=1', function (t) {
     setup(1);
     calcSize(req, {}, function () {
-      t.equal(req.clean.querySize, 1);
+      t.equal(req.clean.querySize, 20);
       t.end();
     });
   });
@@ -46,6 +46,14 @@ module.exports.tests.valid = function(test, common) {
     });
   });
 
+  test('size=20', function (t) {
+    setup(20);
+    calcSize(req, {}, function () {
+      t.equal(req.clean.querySize, 40);
+      t.end();
+    });
+  });
+
   test('no size', function (t) {
     setup();
     calcSize(req, {}, function () {