Add Double Linear testcases

Author: timgrein

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

@@ -80,8 +80,12 @@ public static Iterable<Object[]> parameters() {
         testCaseSuppliers.addAll(longTestCase(300000L, 10L, 10000000L, 200L, 0.33, "gauss", 0.9990040963055015));
         testCaseSuppliers.addAll(longTestCase(123456789112123L, 10L, 10000000L, 200L, 0.33, "gauss", 0.0));
 
-        // Double
-        testCaseSuppliers.addAll(doubleTestCase(5.0, 10.0, 10.0, 0.0, 0.5, "linear", 0.75));
+        // Double Linear
+        testCaseSuppliers.addAll(doubleTestCase(0.0, 10.0, 10000000.0, 200.0, 0.25, "linear", 1.0));
+        testCaseSuppliers.addAll(doubleTestCase(10.0, 10.0, 10000000.0, 200.0, 0.25, "linear", 1.0));
+        testCaseSuppliers.addAll(doubleTestCase(50000.0, 10.0, 10000000.0, 200.0, 0.25, "linear", 0.99626575));
+        testCaseSuppliers.addAll(doubleTestCase(300000.0, 10.0, 10000000.0, 200.0, 0.25, "linear", 0.97751575));
+        testCaseSuppliers.addAll(doubleTestCase(123456789112.123, 10.0, 10000000.0, 200.0, 0.25, "linear", 0.0));
 
         // GeoPoint
         testCaseSuppliers.addAll(geoPointTestCase("POINT (1 1)", "POINT (1 1)", "200km", "0km", 0.5, "linear", 1.0));