update;

src/main/java/rocks/zipcode/quiz3a/fundamentals/StringUtils.java

     public static String removeConsecutiveDuplicateCharacters(String str) {
         return null;
     }
+
+    public static String invertCasing(String str) {
+        return null;
+    }
 }

src/test/java/rocks/zipcode/quiz3a/fundamentals/stringutils/CapitalizeMiddleCharacterTest.java

+package rocks.zipcode.quiz3a.fundamentals.stringutils;
+
+import org.junit.Assert;
+import org.junit.Test;
+import rocks.zipcode.quiz3a.fundamentals.StringUtils;
+
+public class CapitalizeMiddleCharacterTest {
+    @Test
+    public void test1() {
+        // given
+        String input = "o";
+        String expected = "O";
+
+        // when
+        String actual = StringUtils.capitalizeMiddleCharacter(input);
+
+        // then
+        Assert.assertEquals(expected, actual);
+    }
+
+    @Test
+    public void test2() {
+        // given
+        String input = "ooo";
+        String expected = "oOo";
+
+        // when
+        String actual = StringUtils.capitalizeMiddleCharacter(input);
+
+        // then
+        Assert.assertEquals(expected, actual);
+    }
+}

src/test/java/rocks/zipcode/quiz3a/fundamentals/stringutils/GetMiddleCharacterTest.java

+package rocks.zipcode.quiz3a.fundamentals.stringutils;
+
+import org.junit.Assert;
+import org.junit.Test;
+import rocks.zipcode.quiz3a.fundamentals.StringUtils;
+
+public class GetMiddleCharacterTest {
+    @Test
+    public void test1() {
+        // given
+        String input = "joint";
+        Character expected = 'i';
+
+        // when
+        Character actual = StringUtils.getMiddleCharacter(input);
+
+        // then
+        Assert.assertEquals(expected, actual);
+    }
+
+
+    @Test
+    public void test2() {
+        // given
+        String input = "burnt";
+        Character expected = 'r';
+
+        // when
+        Character actual = StringUtils.getMiddleCharacter(input);
+
+        // then
+        Assert.assertEquals(expected, actual);
+    }
+}

src/test/java/rocks/zipcode/quiz3a/fundamentals/stringutils/HasDuplicateCharacterTest.java

+package rocks.zipcode.quiz3a.fundamentals.stringutils;
+
+import org.junit.Assert;
+import org.junit.Test;
+import rocks.zipcode.quiz3a.fundamentals.StringUtils;
+
+public class HasDuplicateCharacterTest {
+    @Test
+    public void test1() {
+        String input = "Happy";
+        Assert.assertFalse(StringUtils.hasDuplicateCharacters(input));
+    }
+
+    @Test
+    public void test2() {
+        String input = "Fool";
+        Assert.assertTrue(StringUtils.hasDuplicateCharacters(input));
+    }
+
+    @Test
+    public void test3() {
+        String input = "George";
+        Assert.assertFalse(StringUtils.hasDuplicateCharacters(input));
+    }
+
+    @Test
+    public void test4() {
+        String input = "False";
+        Assert.assertFalse(StringUtils.hasDuplicateCharacters(input));
+    }
+}

src/test/java/rocks/zipcode/quiz3a/fundamentals/stringutils/InvertCasingTest.java

+package rocks.zipcode.quiz3a.fundamentals.stringutils;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import static rocks.zipcode.quiz3a.fundamentals.StringUtils.invertCasing;
+
+public class InvertCasingTest {
+    @Test
+    public void test0() {
+        String input = "a";
+        String expected = "A";
+        Assert.assertEquals(expected, invertCasing(input));
+    }
+
+    @Test
+    public void test1() {
+        String input = "Z";
+        String expected = "z";
+        Assert.assertEquals(expected, invertCasing(input));
+    }
+
+    @Test
+    public void test2() {
+        String expected = "This one is kind of tricky!";
+        Assert.assertEquals(expected, invertCasing(invertCasing(expected)));
+
+    }
+
+    @Test
+    public void test3() {
+        String input = "iNcReAsInG";
+        String expected = "InCrEaSiNg";
+        Assert.assertEquals(expected, invertCasing(input));
+    }
+
+    @Test
+    public void test4() {
+        String input = "No Big Deal!";
+        String expected = "nO bIG dEAL!";
+        Assert.assertEquals(expected, invertCasing(input));
+    }
+
+    @Test
+    public void test5() {
+        String expected = "#^@!&*$(%$";
+        Assert.assertEquals(expected, invertCasing(expected));
+    }
+}

src/test/java/rocks/zipcode/quiz3a/fundamentals/stringutils/IsIsoGramTest.java

 package rocks.zipcode.quiz3a.fundamentals.stringutils;
 
+import org.junit.Assert;
+import org.junit.Test;
+import rocks.zipcode.quiz3a.fundamentals.StringUtils;
+
 public class IsIsoGramTest {
+    @Test
+    public void test1() {
+        String input = "Jump";
+        Assert.assertTrue(StringUtils.isIsogram(input));
+    }
+
+    @Test
+    public void test2() {
+        String input = "Jj";
+        Assert.assertTrue(StringUtils.isIsogram(input));
+    }
+
+    @Test
+    public void test3() {
+        String input = "Here";
+        Assert.assertFalse(StringUtils.isIsogram(input));
+    }
+
+    @Test
+    public void test4() {
+        String input = "Teared";
+        Assert.assertFalse(StringUtils.isIsogram(input));
+    }
 }

src/test/java/rocks/zipcode/quiz3a/fundamentals/stringutils/LowerCaseMiddleCharacterTest.java

+package rocks.zipcode.quiz3a.fundamentals.stringutils;
+
+import org.junit.Assert;
+import org.junit.Test;
+import rocks.zipcode.quiz3a.fundamentals.StringUtils;
+
+public class LowerCaseMiddleCharacterTest {
+    @Test
+    public void test1() {
+        // given
+        String input = "O";
+        String expected = "o";
+
+        // when
+        String actual = StringUtils.capitalizeMiddleCharacter(input);
+
+        // then
+        Assert.assertEquals(expected, actual);
+    }
+
+    @Test
+    public void test2() {
+        // given
+        String input = "OOO";
+        String expected = "OoO";
+
+        // when
+        String actual = StringUtils.capitalizeMiddleCharacter(input);
+
+        // then
+        Assert.assertEquals(expected, actual);
+    }
+}

src/test/java/rocks/zipcode/quiz3a/fundamentals/stringutils/RemoveDuplicateCharactersTest.java

+package rocks.zipcode.quiz3a.fundamentals.stringutils;
+
+import org.junit.Assert;
+import org.junit.Test;
+import rocks.zipcode.quiz3a.fundamentals.StringUtils;
+
+public class RemoveDuplicateCharactersTest {
+    @Test
+    public void test1() {
+        // given
+        String input = "Fool";
+        String expected = "Fl";
+
+        // when
+        String actual = StringUtils.removeConsecutiveDuplicateCharacters(input);
+
+        // then
+        Assert.assertEquals(expected, actual);
+    }
+
+    @Test
+    public void test2() {
+        // given
+        String input = "Mississippi";
+        String expected = "Miiii";
+
+        // when
+        String actual = StringUtils.removeConsecutiveDuplicateCharacters(input);
+
+        // then
+        Assert.assertEquals(expected, actual);
+    }
+}