add end-to-end test for custom function

jackson-jq/src/test/java/net/thisptr/jackson/jq/CustomFunctionTest.java

@@ -0,0 +1,51 @@
+package net.thisptr.jackson.jq;
+
+import com.fasterxml.jackson.databind.JsonNode;
+import com.fasterxml.jackson.databind.ObjectMapper;
+import com.fasterxml.jackson.databind.node.IntNode;
+import com.fasterxml.jackson.databind.node.ObjectNode;
+import net.thisptr.jackson.jq.exception.JsonQueryException;
+import net.thisptr.jackson.jq.path.Path;
+import org.junit.jupiter.api.Test;
+
+import java.util.ArrayList;
+import java.util.List;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+// end-to-end test of custom function
+public class CustomFunctionTest {
+
+    @Test
+    public void testCustomFunction() throws Exception {
+
+        ObjectMapper mapper = new ObjectMapper();
+        Version version = Versions.JQ_1_6;
+
+        Scope rootScope = Scope.newEmptyScope();
+
+        BuiltinFunctionLoader.getInstance().loadFunctions(version, rootScope);
+
+        rootScope.addFunction("times100", 1, new Function() {
+            @Override
+            public void apply(Scope scope, List<Expression> args, JsonNode in, Path path, PathOutput output, Version version) throws JsonQueryException {
+                args.get(0).apply(scope, in, (numberNode) -> {
+                    assert (numberNode.isIntegralNumber());
+                    output.emit(new IntNode(numberNode.asInt() * 100), null);
+                });
+            }
+        });
+
+        String input = "{ \"a\": 5 }";
+
+        Scope childScope = Scope.newChildScope(rootScope);
+
+        JsonQuery query = JsonQuery.compile("{ \"a\": times100(.a) }", version);
+
+        final List<JsonNode> out = new ArrayList<>();
+        query.apply(childScope, mapper.readTree(input), out::add);
+        assertThat(out).hasSize(1);
+        assertThat(out.get(0)).isInstanceOf(ObjectNode.class);
+        assertThat(out.get(0).toString()).isEqualTo("{\"a\":500}");
+    }
+}