[feat] Add test for the StringChangeNextWord class

Thois commit adds a start for tests for the StringChangeNextWord class.

[issue: #9]

src/test/java/org/jabref/logic/util/strings/StringChangeNextWordTest.java

@@ -0,0 +1,27 @@
+package org.jabref.logic.util.strings;
+
+import org.jabref.logic.util.strings.StringChangeNextWord;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class StringChangeNextWordTest {
+
+    @Test
+    public void editNextWordCapitalizePreservesNewlines() {
+        int pos = 3;
+        String textInput = "hello\nhello";
+        String whatTextShouldBe = "hello\nHello";
+        String textOutput = new StringChangeNextWord().editNextWordCapitalize(pos, textInput);
+        assertEquals(textOutput, whatTextShouldBe);
+    }
+
+    @Test
+    public void editNextWordUpperCaseEditsTheNextWord() {
+        int pos = 3;
+        String textInput = "hello hello";
+        String whatTextShouldBe = "hello HELLO";
+        String textOutput = new StringChangeNextWord().editNextWordUpperCase(pos, textInput);
+        assertEquals(textOutput, whatTextShouldBe);
+    }
+}