Add Double Gaussian testcases

Author: timgrein

x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/fulltext/DecayTests.java

@@ -94,6 +94,13 @@ public static Iterable<Object[]> parameters() {
         testCaseSuppliers.addAll(doubleTestCase(300000.0, 10.0, 10000000.0, 200.0, 0.25, "exp", 0.959292046002994));
         testCaseSuppliers.addAll(doubleTestCase(123456789112.123, 10.0, 10000000.0, 200.0, 0.25, "exp", 0.0));
 
+        // Double Gaussian
+        testCaseSuppliers.addAll(doubleTestCase(0.0, 10.0, 10000000.0, 200.0, 0.25, "gauss", 1.0));
+        testCaseSuppliers.addAll(doubleTestCase(10.0, 10.0, 10000000.0, 200.0, 0.25, "gauss", 1.0));
+        testCaseSuppliers.addAll(doubleTestCase(50000.0, 10.0, 10000000.0, 200.0, 0.25, "gauss", 0.9999656337419655));
+        testCaseSuppliers.addAll(doubleTestCase(300000.0, 10.0, 10000000.0, 200.0, 0.25, "gauss", 0.9987548570291238));
+        testCaseSuppliers.addAll(doubleTestCase(123456789112.123, 10.0, 10000000.0, 200.0, 0.25, "gauss", 0.0));
+
         // GeoPoint
         testCaseSuppliers.addAll(geoPointTestCase("POINT (1 1)", "POINT (1 1)", "200km", "0km", 0.5, "linear", 1.0));
         testCaseSuppliers.addAll(geoPointTestCaseKeywordScale("POINT (1 1)", "POINT (1 1)", "200km", "0km", 0.5, "linear", 1.0));