Increase code coverage.
diff --git a/src/test/java/org/apache/commons/text/matcher/StringMatcherFactoryTest.java b/src/test/java/org/apache/commons/text/matcher/StringMatcherFactoryTest.java
index 58bb279..06f1e0e 100644
--- a/src/test/java/org/apache/commons/text/matcher/StringMatcherFactoryTest.java
+++ b/src/test/java/org/apache/commons/text/matcher/StringMatcherFactoryTest.java
@@ -17,6 +17,7 @@
 
 package org.apache.commons.text.matcher;
 
+import static org.junit.jupiter.api.Assertions.assertEquals;
 import static org.junit.jupiter.api.Assertions.assertNotNull;
 
 import org.junit.jupiter.api.Test;
@@ -30,76 +31,120 @@
     public void test_andMatcher() {
         assertNotNull(StringMatcherFactory.INSTANCE.andMatcher(StringMatcherFactory.INSTANCE.charMatcher('1'),
             StringMatcherFactory.INSTANCE.stringMatcher("2")));
+        assertNotNull(StringMatcherFactory.INSTANCE.andMatcher(null, StringMatcherFactory.INSTANCE.stringMatcher("2")));
+        assertNotNull(StringMatcherFactory.INSTANCE.andMatcher(null, null));
     }
 
     @Test
     public void test_charMatcher() {
-        assertNotNull(StringMatcherFactory.INSTANCE.charMatcher('1'));
+        final StringMatcher charMatcher = StringMatcherFactory.INSTANCE.charMatcher('1');
+        assertNotNull(charMatcher);
+        assertNotNull(charMatcher.toString());
+        assertEquals(1, charMatcher.size());
     }
 
     @Test
     public void test_charSetMatcher_char() {
-        assertNotNull(StringMatcherFactory.INSTANCE.charSetMatcher('1'));
+        final StringMatcher charSetMatcher = StringMatcherFactory.INSTANCE.charSetMatcher('1');
+        assertNotNull(charSetMatcher);
+        assertNotNull(charSetMatcher.toString());
+        assertEquals(1, charSetMatcher.size());
     }
 
     @Test
     public void test_charSetMatcher_String() {
-        assertNotNull(StringMatcherFactory.INSTANCE.charSetMatcher("1"));
+        final StringMatcher charSetMatcher = StringMatcherFactory.INSTANCE.charSetMatcher("1");
+        assertNotNull(charSetMatcher);
+        assertNotNull(charSetMatcher.toString());
+        assertEquals(1, charSetMatcher.size());
     }
 
     @Test
     public void test_commaMatcher() {
-        assertNotNull(StringMatcherFactory.INSTANCE.commaMatcher());
+        final StringMatcher commaMatcher = StringMatcherFactory.INSTANCE.commaMatcher();
+        assertNotNull(commaMatcher);
+        assertNotNull(commaMatcher.toString());
+        assertEquals(1, commaMatcher.size());
     }
 
     @Test
     public void test_doubleQuoteMatcher() {
-        assertNotNull(StringMatcherFactory.INSTANCE.doubleQuoteMatcher());
+        final StringMatcher doubleQuoteMatcher = StringMatcherFactory.INSTANCE.doubleQuoteMatcher();
+        assertNotNull(doubleQuoteMatcher);
+        assertNotNull(doubleQuoteMatcher.toString());
+        assertEquals(1, doubleQuoteMatcher.size());
     }
 
     @Test
     public void test_noneMatcher() {
-        assertNotNull(StringMatcherFactory.INSTANCE.noneMatcher());
+        final StringMatcher noneMatcher = StringMatcherFactory.INSTANCE.noneMatcher();
+        assertNotNull(noneMatcher);
+        assertNotNull(noneMatcher.toString());
+        assertEquals(0, noneMatcher.size());
     }
 
     @Test
     public void test_quoteMatcher() {
-        assertNotNull(StringMatcherFactory.INSTANCE.quoteMatcher());
+        final StringMatcher quoteMatcher = StringMatcherFactory.INSTANCE.quoteMatcher();
+        assertNotNull(quoteMatcher);
+        assertNotNull(quoteMatcher.toString());
+        assertEquals(1, quoteMatcher.size());
     }
 
     @Test
     public void test_singleQuoteMatcher() {
-        assertNotNull(StringMatcherFactory.INSTANCE.singleQuoteMatcher());
+        final StringMatcher singleQuoteMatcher = StringMatcherFactory.INSTANCE.singleQuoteMatcher();
+        assertNotNull(singleQuoteMatcher);
+        assertNotNull(singleQuoteMatcher.toString());
+        assertEquals(1, singleQuoteMatcher.size());
     }
 
     @Test
     public void test_spaceMatcher() {
-        assertNotNull(StringMatcherFactory.INSTANCE.spaceMatcher());
+        final StringMatcher spaceMatcher = StringMatcherFactory.INSTANCE.spaceMatcher();
+        assertNotNull(spaceMatcher);
+        assertNotNull(spaceMatcher.toString());
+        assertEquals(1, spaceMatcher.size());
     }
 
     @Test
     public void test_splitMatcher() {
-        assertNotNull(StringMatcherFactory.INSTANCE.splitMatcher());
+        final StringMatcher splitMatcher = StringMatcherFactory.INSTANCE.splitMatcher();
+        assertNotNull(splitMatcher);
+        assertNotNull(splitMatcher.toString());
+        assertEquals(1, splitMatcher.size());
     }
 
     @Test
     public void test_stringMatcher() {
-        assertNotNull(StringMatcherFactory.INSTANCE.stringMatcher("1"));
+        final StringMatcher stringMatcher = StringMatcherFactory.INSTANCE.stringMatcher("1");
+        assertNotNull(stringMatcher);
+        assertNotNull(stringMatcher.toString());
+        assertEquals(1, stringMatcher.size());
     }
 
     @Test
     public void test_stringMatcherChars() {
-        assertNotNull(StringMatcherFactory.INSTANCE.stringMatcher('1', '2'));
+        final StringMatcher stringMatcher = StringMatcherFactory.INSTANCE.stringMatcher('1', '2');
+        assertNotNull(stringMatcher);
+        assertNotNull(stringMatcher.toString());
+        assertEquals(2, stringMatcher.size());
     }
 
     @Test
     public void test_tabMatcher() {
-        assertNotNull(StringMatcherFactory.INSTANCE.charMatcher('1'));
+        final StringMatcher charMatcher = StringMatcherFactory.INSTANCE.charMatcher('1');
+        assertNotNull(charMatcher);
+        assertNotNull(charMatcher.toString());
+        assertEquals(1, charMatcher.size());
     }
 
     @Test
     public void test_trimMatcher() {
-        assertNotNull(StringMatcherFactory.INSTANCE.charMatcher('1'));
+        final StringMatcher charMatcher = StringMatcherFactory.INSTANCE.charMatcher('1');
+        assertNotNull(charMatcher);
+        assertNotNull(charMatcher.toString());
+        assertEquals(1, charMatcher.size());
     }
 
 }
diff --git a/src/test/java/org/apache/commons/text/matcher/StringMatcherOnCharArrayTest.java b/src/test/java/org/apache/commons/text/matcher/StringMatcherOnCharArrayTest.java
index 750acaa..6fb9e94 100644
--- a/src/test/java/org/apache/commons/text/matcher/StringMatcherOnCharArrayTest.java
+++ b/src/test/java/org/apache/commons/text/matcher/StringMatcherOnCharArrayTest.java
@@ -32,12 +32,7 @@
 
     private static final int INPUT2_LENGTH = INPUT2.length;
 
-    @Test
-    public void testAndMatcher_char() {
-        final StringMatcher matcher = StringMatcherFactory.INSTANCE.andMatcher(
-            StringMatcherFactory.INSTANCE.charMatcher('c'), StringMatcherFactory.INSTANCE.stringMatcher("de"));
-        assertEquals(3, matcher.size());
-        //
+    private void checkAndMatcher_char(final StringMatcher matcher) {
         assertThat(matcher.isMatch(INPUT2, 0, 0, INPUT2_LENGTH)).isEqualTo(0);
         assertThat(matcher.isMatch(INPUT2, 1, 0, INPUT2_LENGTH)).isEqualTo(0);
         assertThat(matcher.isMatch(INPUT2, 2, 0, INPUT2_LENGTH)).isEqualTo(3);
@@ -54,6 +49,18 @@
     }
 
     @Test
+    public void testAndMatcher_char() {
+        final StringMatcher matcher1 = StringMatcherFactory.INSTANCE.andMatcher(
+            StringMatcherFactory.INSTANCE.charMatcher('c'), StringMatcherFactory.INSTANCE.stringMatcher("de"));
+        assertEquals(3, matcher1.size());
+        checkAndMatcher_char(matcher1);
+        final StringMatcher matcher2 = StringMatcherFactory.INSTANCE.andMatcher(null, StringMatcherFactory.INSTANCE.charMatcher('c'), null,
+            StringMatcherFactory.INSTANCE.stringMatcher("de"), null);
+        assertEquals(3, matcher1.size());
+        checkAndMatcher_char(matcher2);
+    }
+
+    @Test
     public void testCharMatcher_char() {
         final StringMatcher matcher = StringMatcherFactory.INSTANCE.charMatcher('c');
         assertEquals(1, matcher.size());
diff --git a/src/test/java/org/apache/commons/text/matcher/StringMatcherOnCharSequenceStringTest.java b/src/test/java/org/apache/commons/text/matcher/StringMatcherOnCharSequenceStringTest.java
index de89159..d4fa2e9 100644
--- a/src/test/java/org/apache/commons/text/matcher/StringMatcherOnCharSequenceStringTest.java
+++ b/src/test/java/org/apache/commons/text/matcher/StringMatcherOnCharSequenceStringTest.java
@@ -32,12 +32,7 @@
 
     private static final int INPUT2_LENGTH = INPUT2.length();
 
-    @Test
-    public void testAndMatcher_char() {
-        final StringMatcher matcher = StringMatcherFactory.INSTANCE.andMatcher(
-            StringMatcherFactory.INSTANCE.charMatcher('c'), StringMatcherFactory.INSTANCE.stringMatcher("de"));
-        assertEquals(3, matcher.size());
-        //
+    private void checkAndMatcher_char(final StringMatcher matcher) {
         assertThat(matcher.isMatch(INPUT2, 0, 0, INPUT2_LENGTH)).isEqualTo(0);
         assertThat(matcher.isMatch(INPUT2, 1, 0, INPUT2_LENGTH)).isEqualTo(0);
         assertThat(matcher.isMatch(INPUT2, 2, 0, INPUT2_LENGTH)).isEqualTo(3);
@@ -54,6 +49,19 @@
     }
 
     @Test
+    public void testAndMatcher_char() {
+        final StringMatcher matcher1 = StringMatcherFactory.INSTANCE.andMatcher(
+            StringMatcherFactory.INSTANCE.charMatcher('c'), StringMatcherFactory.INSTANCE.stringMatcher("de"));
+        assertEquals(3, matcher1.size());
+        checkAndMatcher_char(matcher1);
+        final StringMatcher matcher2 = StringMatcherFactory.INSTANCE.andMatcher(null,
+            StringMatcherFactory.INSTANCE.charMatcher('c'), null, StringMatcherFactory.INSTANCE.stringMatcher("de"),
+            null);
+        assertEquals(3, matcher1.size());
+        checkAndMatcher_char(matcher2);
+    }
+
+    @Test
     public void testCharMatcher_char() {
         final StringMatcher matcher = StringMatcherFactory.INSTANCE.charMatcher('c');
         assertEquals(1, matcher.size());