feat: add new JSON builtin functions (%str2json, %json_add and %json_remove)

From those requests:
- https://forum.plantuml.net/15436/allow-update-json-object-or-array-value
- https://forum.plantuml.net/17474/modify-json-variables-in-preprocessor
- https://forum.plantuml.net/18418/request-%25set_json_keys-function-json-writing-capabilities
- #328
- #1733

src/net/sourceforge/plantuml/tim/TContext.java

@@ -110,7 +110,9 @@ import net.sourceforge.plantuml.tim.stdlib.IntVal;
 import net.sourceforge.plantuml.tim.stdlib.InvokeProcedure;
 import net.sourceforge.plantuml.tim.stdlib.IsDark;
 import net.sourceforge.plantuml.tim.stdlib.IsLight;
+import net.sourceforge.plantuml.tim.stdlib.JsonAdd;
 import net.sourceforge.plantuml.tim.stdlib.JsonKeyExists;
+import net.sourceforge.plantuml.tim.stdlib.JsonRemove;
 import net.sourceforge.plantuml.tim.stdlib.Lighten;
 import net.sourceforge.plantuml.tim.stdlib.LoadJson;
 import net.sourceforge.plantuml.tim.stdlib.LogicalAnd;
@@ -132,6 +134,7 @@ import net.sourceforge.plantuml.tim.stdlib.SetVariableValue;
 import net.sourceforge.plantuml.tim.stdlib.Size;
 import net.sourceforge.plantuml.tim.stdlib.SplitStr;
 import net.sourceforge.plantuml.tim.stdlib.SplitStrRegex;
+import net.sourceforge.plantuml.tim.stdlib.Str2Json;
 import net.sourceforge.plantuml.tim.stdlib.StringFunction;
 import net.sourceforge.plantuml.tim.stdlib.Strlen;
 import net.sourceforge.plantuml.tim.stdlib.Strpos;
@@ -216,6 +219,9 @@ public class TContext {
 		functionsSet.addFunction(new GetAllTheme());
 		functionsSet.addFunction(new GetAllStdlib());
 		functionsSet.addFunction(new SplitStrRegex());
+		functionsSet.addFunction(new Str2Json());
+		functionsSet.addFunction(new JsonAdd());
+		functionsSet.addFunction(new JsonRemove());
 		// %standard_exists_function
 		// %str_replace
 		// !exit

src/net/sourceforge/plantuml/tim/stdlib/JsonAdd.java

@@ -0,0 +1,89 @@
+/* ========================================================================
+ * PlantUML : a free UML diagram generator
+ * ========================================================================
+ *
+ * (C) Copyright 2009-2021, Arnaud Roques
+ *
+ * Project Info:  https://plantuml.com
+ *
+ * If you like this project or if you find it useful, you can support us at:
+ *
+ * https://plantuml.com/patreon (only 1$ per month!)
+ * https://plantuml.com/paypal
+ *
+ * This file is part of PlantUML.
+ *
+ * PlantUML is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * PlantUML distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
+ * USA.
+ *
+ *
+ * Original Author:  Arnaud Roques
+ * Contribution: The-Lum
+ *
+ */
+package net.sourceforge.plantuml.tim.stdlib;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import net.sourceforge.plantuml.json.JsonArray;
+import net.sourceforge.plantuml.json.JsonObject;
+import net.sourceforge.plantuml.json.JsonValue;
+import net.sourceforge.plantuml.text.StringLocated;
+import net.sourceforge.plantuml.tim.EaterException;
+import net.sourceforge.plantuml.tim.TContext;
+import net.sourceforge.plantuml.tim.TFunctionSignature;
+import net.sourceforge.plantuml.tim.TMemory;
+import net.sourceforge.plantuml.tim.expression.TValue;
+
+public class JsonAdd extends SimpleReturnFunction {
+
+	public TFunctionSignature getSignature() {
+		return new TFunctionSignature("%json_add", 3);
+	}
+
+	@Override
+	public boolean canCover(int nbArg, Set<String> namedArgument) {
+		return nbArg == 2 || nbArg == 3;
+	}
+
+	@Override
+	public TValue executeReturnFunction(TContext context, TMemory memory, StringLocated location, List<TValue> values,
+			Map<String, TValue> named) throws EaterException {
+		final TValue data = values.get(0);
+		if (data.isJson() == false)
+			throw new EaterException("Not JSON data", location);
+
+		final JsonValue json = data.toJson();
+
+		if (!json.isArray() && !json.isObject())
+			return data;
+		if (json.isArray()) {
+			final JsonValue value = values.get(1).toJson();
+			final JsonArray array = (JsonArray) json;
+			array.add(value);
+			return TValue.fromJson(array);
+		}
+		if (json.isObject()) {
+			final String name = values.get(1).toString();
+			final JsonValue value = values.get(2).toJson();
+			final JsonObject object = (JsonObject) json;
+			object.add(name, value);
+			return TValue.fromJson(object);
+		}
+		throw new EaterException("Bad JSON type", location);
+	}
+}

src/net/sourceforge/plantuml/tim/stdlib/JsonRemove.java

@@ -0,0 +1,91 @@
+/* ========================================================================
+ * PlantUML : a free UML diagram generator
+ * ========================================================================
+ *
+ * (C) Copyright 2009-2021, Arnaud Roques
+ *
+ * Project Info:  https://plantuml.com
+ *
+ * If you like this project or if you find it useful, you can support us at:
+ *
+ * https://plantuml.com/patreon (only 1$ per month!)
+ * https://plantuml.com/paypal
+ *
+ * This file is part of PlantUML.
+ *
+ * PlantUML is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * PlantUML distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
+ * USA.
+ *
+ *
+ * Original Author:  Arnaud Roques
+ * Contribution: The-Lum
+ *
+ */
+package net.sourceforge.plantuml.tim.stdlib;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import net.sourceforge.plantuml.json.JsonArray;
+import net.sourceforge.plantuml.json.JsonObject;
+import net.sourceforge.plantuml.json.JsonValue;
+import net.sourceforge.plantuml.text.StringLocated;
+import net.sourceforge.plantuml.tim.EaterException;
+import net.sourceforge.plantuml.tim.TContext;
+import net.sourceforge.plantuml.tim.TFunctionSignature;
+import net.sourceforge.plantuml.tim.TMemory;
+import net.sourceforge.plantuml.tim.expression.TValue;
+
+public class JsonRemove extends SimpleReturnFunction {
+
+	public TFunctionSignature getSignature() {
+		return new TFunctionSignature("%json_remove", 2);
+	}
+
+	@Override
+	public boolean canCover(int nbArg, Set<String> namedArgument) {
+		return nbArg == 2;
+	}
+
+	@Override
+	public TValue executeReturnFunction(TContext context, TMemory memory, StringLocated location, List<TValue> values,
+			Map<String, TValue> named) throws EaterException {
+		final TValue data = values.get(0);
+		if (data.isJson() == false)
+			throw new EaterException("Not JSON data", location);
+		
+		final JsonValue json = data.toJson();
+		
+		if (!json.isArray() && !json.isObject())
+			return data;
+		if (json.isArray()) {
+			final JsonArray array = (JsonArray) json;
+			if (values.get(1).isNumber()) {
+				final Integer index = values.get(1).toInt();
+				if (0 <= index && index < array.size())
+					array.remove(index);
+			}
+			return TValue.fromJson(array);
+		}
+		if (json.isObject()) {
+			final JsonObject object = (JsonObject) json;
+			final String name = values.get(1).toString();
+			object.remove(name);
+			return TValue.fromJson(object);
+		}
+		throw new EaterException("Bad JSON type", location);
+	}
+}

src/net/sourceforge/plantuml/tim/stdlib/Str2Json.java

@@ -0,0 +1,75 @@
+/* ========================================================================
+ * PlantUML : a free UML diagram generator
+ * ========================================================================
+ *
+ * (C) Copyright 2009-2021, Arnaud Roques
+ *
+ * Project Info:  https://plantuml.com
+ *
+ * If you like this project or if you find it useful, you can support us at:
+ *
+ * https://plantuml.com/patreon (only 1$ per month!)
+ * https://plantuml.com/paypal
+ *
+ * This file is part of PlantUML.
+ *
+ * PlantUML is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or
+ * (at your option) any later version.
+ *
+ * PlantUML distributed in the hope that it will be useful, but
+ * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
+ * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU General Public
+ * License along with this library; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
+ * USA.
+ *
+ *
+ * Original Author:  Arnaud Roques
+ * Contribution: The-Lum
+ *
+ */
+package net.sourceforge.plantuml.tim.stdlib;
+
+import java.util.List;
+import java.util.Map;
+import java.util.Set;
+
+import net.sourceforge.plantuml.json.Json;
+import net.sourceforge.plantuml.json.JsonArray;
+import net.sourceforge.plantuml.json.JsonObject;
+import net.sourceforge.plantuml.json.JsonValue;
+import net.sourceforge.plantuml.text.StringLocated;
+import net.sourceforge.plantuml.tim.EaterException;
+import net.sourceforge.plantuml.tim.TContext;
+import net.sourceforge.plantuml.tim.TFunctionSignature;
+import net.sourceforge.plantuml.tim.TMemory;
+import net.sourceforge.plantuml.tim.expression.TValue;
+
+public class Str2Json extends SimpleReturnFunction {
+
+	public TFunctionSignature getSignature() {
+		return new TFunctionSignature("%str2json", 1);
+	}
+
+	@Override
+	public boolean canCover(int nbArg, Set<String> namedArgument) {
+		return nbArg == 1;
+	}
+
+	@Override
+	public TValue executeReturnFunction(TContext context, TMemory memory, StringLocated location, List<TValue> values,
+			Map<String, TValue> named) throws EaterException {
+		try {
+			final String value = values.get(0).toString();
+			final JsonValue json = Json.parse(value);
+			return TValue.fromJson(json);
+		} catch (Throwable t) {
+			return TValue.fromString("");
+		}
+	}
+}

test/net/sourceforge/plantuml/tim/TimTestUtils.java

@@ -16,21 +16,28 @@ public class TimTestUtils {
 
 	// Tfunc: () -> (String)
 	public static void assertTimExpectedOutput(TFunction func, String expected) throws EaterException {
-		TValue tValue = func.executeReturnFunction(null, null, null, null, null);
+		final TValue tValue = func.executeReturnFunction(null, null, null, Collections.emptyList(), null);
 		assertEquals(expected, tValue.toString());
 	}
 
 	// Tfunc: (Integer) -> (String)
 	public static void assertTimExpectedOutputFromInput(TFunction func, Integer input, String expected) throws EaterException {
-		List<TValue> values = Collections.singletonList(TValue.fromInt(input));
-		TValue tValue = func.executeReturnFunction(null, null, null, values, null);
+		final List<TValue> values = Collections.singletonList(TValue.fromInt(input));
+		final TValue tValue = func.executeReturnFunction(null, null, null, values, null);
+		assertEquals(expected, tValue.toString());
+	}
+
+	// Tfunc: (Integer, Integer) -> (String)
+	public static void assertTimExpectedOutputFromInput(TFunction func, Integer input1, Integer input2, String expected) throws EaterException {
+		final List<TValue> values = Arrays.asList(TValue.fromInt(input1), TValue.fromInt(input2));
+		final TValue tValue = func.executeReturnFunction(null, null, null, values, null);
 		assertEquals(expected, tValue.toString());
 	}
 
 	// Tfunc: (String) -> (String)
 	public static void assertTimExpectedOutputFromInput(TFunction func, String input, String expected) throws EaterException {
-		List<TValue> values = Collections.singletonList(TValue.fromString(input));
-		TValue tValue = func.executeReturnFunction(null, null, null, values, null);
+		final List<TValue> values = Collections.singletonList(TValue.fromString(input));
+		final TValue tValue = func.executeReturnFunction(null, null, null, values, null);
 		assertEquals(expected, tValue.toString());
 	}
 
@@ -43,8 +50,36 @@ public class TimTestUtils {
 
 	// Tfunc: (JsonValue) -> (String)
 	public static void assertTimExpectedOutputFromInput(TFunction func, JsonValue input, String expected) throws EaterException {
-		List<TValue> values = Collections.singletonList(TValue.fromJson(input));
-		TValue tValue = func.executeReturnFunction(null, null, null, values, null);
+		final List<TValue> values = Collections.singletonList(TValue.fromJson(input));
+		final TValue tValue = func.executeReturnFunction(null, null, null, values, null);
+		assertEquals(expected, tValue.toString());
+	}
+	
+	// Tfunc: (JsonValue, JsonValue) -> (String)
+	public static void assertTimExpectedOutputFromInput(TFunction func, JsonValue input1,  JsonValue input2, String expected) throws EaterException {
+		final List<TValue> values = Arrays.asList(TValue.fromJson(input1), TValue.fromJson(input2));
+		final TValue tValue = func.executeReturnFunction(null, null, null, values, null);
+		assertEquals(expected, tValue.toString());
+	}
+
+	// Tfunc: (JsonValue, Int) -> (String)
+	public static void assertTimExpectedOutputFromInput(TFunction func, JsonValue input1,  Integer input2, String expected) throws EaterException {
+		final List<TValue> values = Arrays.asList(TValue.fromJson(input1), TValue.fromInt(input2));
+		final TValue tValue = func.executeReturnFunction(null, null, null, values, null);
+		assertEquals(expected, tValue.toString());
+	}
+
+	// Tfunc: (JsonValue, String) -> (String)
+	public static void assertTimExpectedOutputFromInput(TFunction func, JsonValue input1,  String input2, String expected) throws EaterException {
+		final List<TValue> values = Arrays.asList(TValue.fromJson(input1), TValue.fromString(input2));
+		final TValue tValue = func.executeReturnFunction(null, null, null, values, null);
+		assertEquals(expected, tValue.toString());
+	}
+
+	// Tfunc: (JsonValue, String, JsonValue) -> (String)
+	public static void assertTimExpectedOutputFromInput(TFunction func, JsonValue input1,  String input2, JsonValue input3, String expected) throws EaterException {
+		final List<TValue> values = Arrays.asList(TValue.fromJson(input1), TValue.fromString(input2), TValue.fromJson(input3));
+		final TValue tValue = func.executeReturnFunction(null, null, null, values, null);
 		assertEquals(expected, tValue.toString());
 	}
 

test/net/sourceforge/plantuml/tim/stdlib/JsonAddTest.java

@@ -0,0 +1,117 @@
+package net.sourceforge.plantuml.tim.stdlib;
+
+import static net.sourceforge.plantuml.tim.TimTestUtils.assertTimExpectedOutputFromInput;
+
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.DisplayNameGenerator.ReplaceUnderscores;
+import org.junit.jupiter.api.IndicativeSentencesGeneration;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.converter.ConvertWith;
+import org.junit.jupiter.params.provider.CsvSource;
+
+import net.sourceforge.plantuml.json.JsonValue;
+import net.sourceforge.plantuml.tim.EaterException;
+import net.sourceforge.plantuml.tim.TFunction;
+import test.utils.JunitUtils.StringJsonConverter;
+
+/**
+ * Tests the builtin function.
+ */
+@IndicativeSentencesGeneration(separator = ": ", generator = ReplaceUnderscores.class)
+
+class JsonAddTest {
+	TFunction cut = new JsonAdd();
+	final String cutName = "json_add";
+	final String paramTestName = "[{index}] " + cutName + "({0}, {1}) = {2}";
+
+	@ParameterizedTest(name = paramTestName)
+	@CsvSource(value = {
+			"  [],                1,            [1]",
+			"  [0],               \"a\",        '[0,\"a\"]' ",
+			"  [0],               {\"a\": 123}, '[0,{\"a\":123}]' ",
+			"  [0],               [1],          '[0,[1]]' ",
+			" '[{\"a\":[1, 2]}]', 1,            '[{\"a\":[1,2]},1]' ",
+
+	})
+	void Test_with_Array_Json(@ConvertWith(StringJsonConverter.class) JsonValue input1, @ConvertWith(StringJsonConverter.class) JsonValue input2, String expected) throws EaterException {
+		assertTimExpectedOutputFromInput(cut, input1, input2, expected);
+	}
+	
+	@ParameterizedTest(name = "[{index}] " + cutName + "({0}, {1}, {2}) = {3}")
+	@CsvSource(value = {
+			" {}, a, 1,  {\"a\":1}",
+			" {}, a, '[1,2,3]',  '{\"a\":[1,2,3]}'",
+			" {}, a, '{\"b\":123}',  '{\"a\":{\"b\":123}}'",
+			" {}, a, '{\"b\":\"abc\"}',  '{\"a\":{\"b\":\"abc\"}}'",
+			" {\"z\":0}, a, 1,  '{\"z\":0,\"a\":1}'",
+			" {\"z\":0}, a, '[1,2,3]',  '{\"z\":0,\"a\":[1,2,3]}'",
+			" {\"z\":0}, a, '{\"b\":123}',  '{\"z\":0,\"a\":{\"b\":123}}'",
+			" {\"z\":0}, a, '{\"b\":\"abc\"}',  '{\"z\":0,\"a\":{\"b\":\"abc\"}}'",
+			" '{\"a\": 1, \"b\": \"two\"}', c, 3, '{\"a\":1,\"b\":\"two\",\"c\":3}'",
+			" '{\"a\": 1, \"b\": \"two\"}', d, '{\"da\": 1, \"db\": \"two\"}', '{\"a\":1,\"b\":\"two\",\"d\":{\"da\":1,\"db\":\"two\"}}'",
+
+	})
+	void Test_with_Object_Json(@ConvertWith(StringJsonConverter.class) JsonValue input1, String input2, @ConvertWith(StringJsonConverter.class) JsonValue input3, String expected) throws EaterException {
+		assertTimExpectedOutputFromInput(cut, input1, input2, input3, expected);
+	}
+
+	@Nested
+	class Not_Nominal_Test {
+		@ParameterizedTest(name = paramTestName)
+		@CsvSource(value = {
+				" 0,     1,     0",
+				" 1,     1,     1",
+				" true,  1,     true",
+				" false, 1,     false",
+				" \"a\", 1,     a",
+				" null,  1,     null",
+				" 0,     \"b\", 0",
+				" 1,     \"b\", 1",
+				" true,  \"b\", true",
+				" false, \"b\", false",
+				" \"a\", \"b\", a",
+				" null,  \"b\", null",
+				" 0,     true,  0",
+				" 1,     true,  1",
+				" true,  true,  true",
+				" false, true,  false",
+				" \"a\", true,  a",
+				" null,  true,  null",
+		})
+		void Test_with_Simple(@ConvertWith(StringJsonConverter.class) JsonValue input1, @ConvertWith(StringJsonConverter.class) JsonValue input2, String expected) throws EaterException {
+			assertTimExpectedOutputFromInput(cut, input1, input2, expected);
+		}
+		@ParameterizedTest(name = paramTestName)
+		@CsvSource(value = {
+				" 0,     1, 0",
+				" 1,     1, 1",
+				" true,  1, true",
+				" false, 1, false",
+				" \"a\", 1, a",
+				" null,  1, null",
+		})
+		void Test_with_Simple(@ConvertWith(StringJsonConverter.class) JsonValue input1, Integer input2, String expected) throws EaterException {
+			assertTimExpectedOutputFromInput(cut, input1, input2, expected);
+		}
+		@ParameterizedTest(name = paramTestName)
+		@CsvSource(value = {
+				" 0,     1, 0",
+				" 1,     1, 1",
+				" true,  1, true",
+				" false, 1, false",
+				" \"a\", 1, a",
+				" null,  1, null",
+				" 0,     b, 0",
+				" 1,     b, 1",
+				" true,  b, true",
+				" false, b, false",
+				" \"a\", b, a",
+				" null,  b, null",
+		})
+		void Test_with_Simple(@ConvertWith(StringJsonConverter.class) JsonValue input1, String input2, String expected) throws EaterException {
+			assertTimExpectedOutputFromInput(cut, input1, input2, expected);
+		}
+	}
+}

test/net/sourceforge/plantuml/tim/stdlib/JsonRemoveTest.java

@@ -0,0 +1,86 @@
+package net.sourceforge.plantuml.tim.stdlib;
+
+import static net.sourceforge.plantuml.tim.TimTestUtils.assertTimExpectedOutputFromInput;
+
+import org.junit.jupiter.api.Disabled;
+import org.junit.jupiter.api.DisplayNameGenerator.ReplaceUnderscores;
+import org.junit.jupiter.api.IndicativeSentencesGeneration;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.converter.ConvertWith;
+import org.junit.jupiter.params.provider.CsvSource;
+
+import net.sourceforge.plantuml.json.JsonValue;
+import net.sourceforge.plantuml.tim.EaterException;
+import net.sourceforge.plantuml.tim.TFunction;
+import test.utils.JunitUtils.StringJsonConverter;
+
+/**
+ * Tests the builtin function.
+ */
+@IndicativeSentencesGeneration(separator = ": ", generator = ReplaceUnderscores.class)
+
+class JsonRemoveTest {
+	TFunction cut = new JsonRemove();
+	final String cutName = "json_remove";
+	final String paramTestName = "[{index}] " + cutName + "({0}, {1}) = {2}";
+
+	@ParameterizedTest(name = paramTestName)
+	@CsvSource(value = {
+			" [], -1,  []",
+			" [], 1,  []",
+			" [0], 0, [] ",
+			" [0], 1, [0] ",
+			" '[1,2,3]', -1,  '[1,2,3]' ", // To debate...
+			" '[1,2,3]', 0,  '[2,3]' ",
+			" '[1,2,3]', 1,  '[1,3]' ",
+			" '[1,2,3]', 2,  '[1,2]' ",
+			" '[1,2,3]', 3,  '[1,2,3]' ",
+			" '[{\"a\":[1, 2]}, 1, \"a\"]', 2, '[{\"a\":[1,2]},1]' ",
+	})
+	void Test_with_Array_Json(@ConvertWith(StringJsonConverter.class) JsonValue input1, Integer input2, String expected) throws EaterException {
+		assertTimExpectedOutputFromInput(cut, input1, input2, expected);
+	}
+	
+	@ParameterizedTest(name = paramTestName)
+	@CsvSource(value = {
+			" '{\"z\":0,\"a\":1}',                                       a, '{\"z\":0}'",
+			" '{\"z\":0,\"a\":1}',                                       b, '{\"z\":0,\"a\":1}'",
+			" '{\"a\": 1, \"b\": \"two\",\"c\":3}',                      c, '{\"a\":1,\"b\":\"two\"}'",
+			" '{\"a\":1,\"b\":\"two\",\"d\":{\"da\":1,\"db\":\"two\"}}', d, '{\"a\":1,\"b\":\"two\"}'",
+
+	})
+	void Test_with_Object_Json(@ConvertWith(StringJsonConverter.class) JsonValue input1, String input2, String expected) throws EaterException {
+		assertTimExpectedOutputFromInput(cut, input1, input2, expected);
+	}
+
+	@Nested
+	class Not_Nominal_Test {
+		@ParameterizedTest(name = paramTestName)
+		@CsvSource(value = {
+				" [],        a,   []",
+				" '[1,2,3]', abc, '[1,2,3]' ",
+				" '[1,2,3]', 1,   '[1,2,3]' ",
+				" 123, 1, 123",
+				" true,  a, true",
+				" true,  1, true",
+				" \"abc\", a, abc",
+				" \"a b c\", a, a b c", 
+				" \"a b c\", 1, a b c",
+		})
+		void Test_with_not_good_type(@ConvertWith(StringJsonConverter.class) JsonValue input1, String input2, String expected) throws EaterException {
+			assertTimExpectedOutputFromInput(cut, input1, input2, expected);
+		}
+
+		@ParameterizedTest(name = paramTestName)
+		@CsvSource(value = {
+				" '{\"z\":0,\"a\":1}',                   5, '{\"z\":0,\"a\":1}'",
+				" '{\"z\":0,\"5\":1}',                   5, '{\"z\":0}'", // Allow cast int -> string
+				" '{\"a\": 1, \"b\": \"two\",\"c\":3}', 10, '{\"a\":1,\"b\":\"two\",\"c\":3}'",
+		})
+		void Test_with_not_good_type(@ConvertWith(StringJsonConverter.class) JsonValue input1, Integer input2, String expected) throws EaterException {
+			assertTimExpectedOutputFromInput(cut, input1, input2, expected);
+		}
+	}
+}

test/net/sourceforge/plantuml/tim/stdlib/Str2JsonTest.java

@@ -0,0 +1,105 @@
+package net.sourceforge.plantuml.tim.stdlib;
+
+import static net.sourceforge.plantuml.tim.TimTestUtils.assertTimExpectedOutput;
+import static net.sourceforge.plantuml.tim.TimTestUtils.assertTimExpectedOutputFromInput;
+
+import org.junit.jupiter.api.DisplayNameGenerator.ReplaceUnderscores;
+import org.junit.jupiter.api.IndicativeSentencesGeneration;
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.converter.ConvertWith;
+import org.junit.jupiter.params.provider.CsvSource;
+
+import net.sourceforge.plantuml.json.JsonValue;
+import net.sourceforge.plantuml.tim.EaterException;
+import net.sourceforge.plantuml.tim.TFunction;
+
+import test.utils.JunitUtils.StringJsonConverter;
+
+/**
+ * Tests the builtin function.
+ */
+@IndicativeSentencesGeneration(separator = ": ", generator = ReplaceUnderscores.class)
+
+class Str2JsonTest {
+	TFunction cut = new Str2Json();
+	final String cutName = "str2json";
+	final String paramTestName = "[{index}] " + cutName + "({0}) = {1}";
+
+	@Test
+	void Test_without_Param() throws EaterException {
+		assertTimExpectedOutput(cut, "");
+	}
+
+	@ParameterizedTest(name = paramTestName)
+	@CsvSource(nullValues = "null", value = {
+			" 0,   0",
+			" -1, -1",
+			" 12, 12",
+	})
+	void Test_with_Integer(Integer input, String expected) throws EaterException {
+		assertTimExpectedOutputFromInput(cut, input, expected);
+	}
+
+	@ParameterizedTest(name = paramTestName)
+	@CsvSource(value = {
+		    " 0, 0 ",
+		    " 1, 1 ",
+		    " 12, 12 ",
+		    " -1, -1 ",
+			" true, true ",
+		    " [true], [true] ",
+			" null, null ",
+			" '', '' ",
+			" \"\", '' ",
+			" a, '' ",
+		    " \"a\", a ",
+		    " '\"a\"', a ",
+		    " \"a b\", a b ",
+		    " 'a b', '' ",
+			" [], [] ",
+			" '[1, 2]', '[1,2]' ",
+			" '[\"a\"]', '[\"a\"]' ",
+			" '{\"a\":[1, 2]}', '{\"a\":[1,2]}' ",
+			" '[{\"a\":[1, 2]}]' , '[{\"a\":[1,2]}]' ",
+			" '{\"a\":\"abc\"}', {\"a\":\"abc\"} ",
+			" '[{\"a\":[1, 2]}, {\"b\":[3, 4]}]', '[{\"a\":[1,2]},{\"b\":[3,4]}]'",
+			" '{\"a\":[1, 2], \"b\":\"abc\", \"b\":true}', '{\"a\":[1,2],\"b\":\"abc\",\"b\":true}'",
+			" '[3, \"different\", { \"types\" : \"of values\" }]', '[3,\"different\",{\"types\":\"of values\"}]'",
+			" '{\"a\": 1, \"b\": \"two\"}', '{\"a\":1,\"b\":\"two\"}' ",
+	})
+	void Test_with_String(String input, String expected) throws EaterException {
+		assertTimExpectedOutputFromInput(cut, input, expected);
+	}
+
+	@ParameterizedTest(name = paramTestName)
+	@CsvSource(value = {
+		    " 0, 0 ",
+		    " 1, 1 ",
+		    " 12, 12 ",
+		    " -1, -1 ",
+			" true, true ",
+		    " [true], [true] ",
+			" null, null ",
+			//" '', '' ",
+			//" \"\", '' ",
+			//" a, '' ",
+		    //" \"a\", a ",
+		    //" '\"a\"', a ",
+		    //" \"a b\", a b ",
+			//" 'a b', a b ",
+			" [], [] ",
+			" '[1, 2]', '[1,2]' ",
+			" '[\"a\"]', '[\"a\"]' ",
+			" '{\"a\":[1, 2]}', '{\"a\":[1,2]}' ",
+			" '[{\"a\":[1, 2]}]' , '[{\"a\":[1,2]}]' ",
+			" '{\"a\":\"abc\"}', {\"a\":\"abc\"} ",
+			" '[{\"a\":[1, 2]}, {\"b\":[3, 4]}]', '[{\"a\":[1,2]},{\"b\":[3,4]}]'",
+			" '{\"a\":[1, 2], \"b\":\"abc\", \"b\":true}', '{\"a\":[1,2],\"b\":\"abc\",\"b\":true}'",
+			" '[3, \"different\", { \"types\" : \"of values\" }]', '[3,\"different\",{\"types\":\"of values\"}]'",
+			" '{\"a\": 1, \"b\": \"two\"}', '{\"a\":1,\"b\":\"two\"}' ",
+	})
+	void Test_with_Json(@ConvertWith(StringJsonConverter.class) JsonValue input, String expected) throws EaterException {
+		assertTimExpectedOutputFromInput(cut, input, expected);
+	}
+}