diff --git a/tests/UnitTests/TemplateSource/TagTests/PluginModifier/PluginModifierImplodeTest.php b/tests/UnitTests/TemplateSource/TagTests/PluginModifier/PluginModifierImplodeTest.php
new file mode 100644
index 00000000..5b816aaf
--- /dev/null
+++ b/tests/UnitTests/TemplateSource/TagTests/PluginModifier/PluginModifierImplodeTest.php
@@ -0,0 +1,44 @@
+<?php
+/**
+ * Smarty PHPunit tests of modifier
+ */
+
+/**
+ * class for modifier tests
+ *
+ * @runTestsInSeparateProcess
+ * @preserveGlobalState    disabled
+ * @backupStaticAttributes enabled
+ */
+class PluginModifierImplodeTest extends PHPUnit_Smarty
+{
+	public function setUp(): void
+	{
+		$this->setUpSmarty(__DIR__);
+	}
+
+	public function testDefault()
+	{
+		$tpl = $this->smarty->createTemplate('string:{""|implode:$v}');
+		$tpl->assign("v", ["1", "2"]);
+		$this->assertEquals("12", $this->smarty->fetch($tpl));
+	}
+	public function testWithSeparator()
+	{
+		$tpl = $this->smarty->createTemplate('string:{","|implode:$v}');
+		$tpl->assign("v", ["a", "b"]);
+		$this->assertEquals("a,b", $this->smarty->fetch($tpl));
+	}
+	public function testInConditional()
+	{
+		$tpl = $this->smarty->createTemplate('string:{if implode("", $v) == "abc"}good{else}bad{/if}');
+		$tpl->assign("v", ['a','b','c']);
+		$this->assertEquals("good", $this->smarty->fetch($tpl));
+	}
+	public function testInConditionalWithSeparator()
+	{
+		$tpl = $this->smarty->createTemplate('string:{if implode("-", $v) == "a-b-c"}good{else}bad{/if}');
+		$tpl->assign("v", ['a','b','c']);
+		$this->assertEquals("good", $this->smarty->fetch($tpl));
+	}
+}
diff --git a/tests/UnitTests/TemplateSource/TagTests/PluginModifier/PluginModifierJsonEncodeTest.php b/tests/UnitTests/TemplateSource/TagTests/PluginModifier/PluginModifierJsonEncodeTest.php
new file mode 100644
index 00000000..965c8a6d
--- /dev/null
+++ b/tests/UnitTests/TemplateSource/TagTests/PluginModifier/PluginModifierJsonEncodeTest.php
@@ -0,0 +1,76 @@
+<?php
+/**
+ * Smarty PHPunit tests of modifier
+ */
+
+/**
+ * class for modifier tests
+ *
+ * @runTestsInSeparateProcess
+ * @preserveGlobalState    disabled
+ * @backupStaticAttributes enabled
+ */
+class PluginModifierJsonEncodeTest extends PHPUnit_Smarty
+{
+	public function setUp(): void
+	{
+		$this->setUpSmarty(__DIR__);
+	}
+
+	/**
+	 * @dataProvider dataForDefault
+	 */
+	public function testDefault($value, $expected)
+	{
+		$tpl = $this->smarty->createTemplate('string:{$v|json_encode}');
+		$tpl->assign("v", $value);
+		$this->assertEquals($expected, $this->smarty->fetch($tpl));
+	}
+
+	/**
+	 * @dataProvider dataForDefault
+	 */
+	public function testDefaultAsFunction($value, $expected)
+	{
+		$tpl = $this->smarty->createTemplate('string:{json_encode($v)}');
+		$tpl->assign("v", $value);
+		$this->assertEquals($expected, $this->smarty->fetch($tpl));
+	}
+
+	public function dataForDefault() {
+		return [
+			["abc", '"abc"'],
+			[["abc"], '["abc"]'],
+			[["abc",["a"=>2]], '["abc",{"a":2}]'],
+		];
+	}
+
+	/**
+	 * @dataProvider dataForForceObject
+	 */
+	public function testForceObject($value, $expected)
+	{
+		$tpl = $this->smarty->createTemplate('string:{$v|json_encode:16}');
+		$tpl->assign("v", $value);
+		$this->assertEquals($expected, $this->smarty->fetch($tpl));
+	}
+
+	/**
+	 * @dataProvider dataForForceObject
+	 */
+	public function testForceObjectAsFunction($value, $expected)
+	{
+		$tpl = $this->smarty->createTemplate('string:{json_encode($v,16)}');
+		$tpl->assign("v", $value);
+		$this->assertEquals($expected, $this->smarty->fetch($tpl));
+	}
+
+	public function dataForForceObject() {
+		return [
+			["abc", '"abc"'],
+			[["abc"], '{"0":"abc"}'],
+			[["abc",["a"=>2]], '{"0":"abc","1":{"a":2}}'],
+		];
+	}
+
+}
diff --git a/tests/UnitTests/TemplateSource/TagTests/PluginModifier/PluginModifierSubstrTest.php b/tests/UnitTests/TemplateSource/TagTests/PluginModifier/PluginModifierSubstrTest.php
new file mode 100644
index 00000000..42abf869
--- /dev/null
+++ b/tests/UnitTests/TemplateSource/TagTests/PluginModifier/PluginModifierSubstrTest.php
@@ -0,0 +1,48 @@
+<?php
+/**
+ * Smarty PHPunit tests of modifier
+ */
+
+/**
+ * class for modifier tests
+ *
+ * @runTestsInSeparateProcess
+ * @preserveGlobalState    disabled
+ * @backupStaticAttributes enabled
+ */
+class PluginModifierSubstrTest extends PHPUnit_Smarty
+{
+	public function setUp(): void
+	{
+		$this->setUpSmarty(__DIR__);
+	}
+
+	public function testDefault()
+	{
+		$tpl = $this->smarty->createTemplate('string:{$v|substr:1}');
+		$tpl->assign("v", "abc");
+		$this->assertEquals("bc", $this->smarty->fetch($tpl));
+	}
+
+	public function testTwoArguments()
+	{
+		$tpl = $this->smarty->createTemplate('string:{$v|substr:1:1}');
+		$tpl->assign("v", "abc");
+		$this->assertEquals("b", $this->smarty->fetch($tpl));
+	}
+
+	public function testNegativeOffset()
+	{
+		$tpl = $this->smarty->createTemplate('string:{$v|substr:-1}');
+		$tpl->assign("v", "abc");
+		$this->assertEquals("c", $this->smarty->fetch($tpl));
+	}
+
+	public function testInConditional()
+	{
+		$tpl = $this->smarty->createTemplate('string:{if substr($v, -1) == "c"}good{else}bad{/if}');
+		$tpl->assign("v", "abc");
+		$this->assertEquals("good", $this->smarty->fetch($tpl));
+	}
+
+}