Painless Context Doc: Add min should match example

relates to elastic#34829

docs/painless/painless-contexts/painless-min-should-match-context.asciidoc

@@ -25,4 +25,53 @@ results.
 
 *API*
 
-The standard <<painless-api-reference, Painless API>> is available.
+The standard <<painless-api-reference, Painless API>> is available.
+
+*Example*
+
+To run this example, first follow the steps in
+<<painless-context-examples, context examples>>.
+
+Imagine that you want to find seats to performances where your favorite
+actors play. You have a list of favorite actors in mind, and you want
+to find performances that have at least certain minimum number of actors
+from your favorite list. `terms_set` query with
+`minimum_should_match_script` is a way to accomplish this. To make
+the query request more configurable, you can define
+`min_actors_to_see` as a script parameter.
+
+To ensure that `min_actors_to_see` parameter doesn't exceed the number
+your favorite actors, use the script below. This script
+selects the minimum value between the parameter `min_actors_to_see` and
+the parameter `num_terms`, which represents the length of the list of
+your favorite actors.
+
+[source,Painless]
+----
+Math.min(params['num_terms'], params['min_actors_to_see'])
+----
+
+Submit the following request to find seats to performances with your favorite actors:
+
+[source,js]
+----
+GET seats/_search
+{
+    "query" : {
+        "terms_set": {
+            "actors" : {
+                "terms" : ["smith", "earns", "black"],
+                "minimum_should_match_script": {
+                    "source": "Math.min(params['num_terms'], params['min_actors_to_see'])",
+                    "params" : {
+                        "min_actors_to_see" : 2
+                    }
+                }
+            }
+        }
+    }
+}
+----
+// CONSOLE
+// TEST[skip: requires setup from other pages]
+

modules/lang-painless/src/test/java/org/elasticsearch/painless/ContextExampleTests.java

@@ -359,5 +359,35 @@ public void testScriptFieldsScript() {
             singletonMap("_source", source), true)
         );
     }
+
+
+    // Use script_fields API to add two extra fields to the hits
+    /*
+    curl -X GET localhost:9200/seats/_search
+    {
+        "query" : {
+            "terms_set": {
+                "actors" : {
+                    "terms" : ["smith", "earns", "black"],
+                    "minimum_should_match_script": {
+                    "source": "Math.min(params['num_terms'], params['min_actors_to_see'])",
+                         "params" : {
+                                "min_actors_to_see" : 2
+                            }
+                    }
+                }
+            }
+        }
+    }
+    */
+    public void testMinShouldMatchScript() {
+        Map<String, Object> params = new HashMap<>();
+        params.put("num_terms", 3);
+        params.put("min_actors_to_see", 2);
+
+        double result = (double) exec("Math.min(params['num_terms'], params['min_actors_to_see']);", params, true);
+        assertEquals(2, result, 0);
+    }
+
 }