[Junie]: test(entry): add unit test for BibEntry.trimLeft()

jablib/src/test/java/org/jabref/model/entry/BibEntryTrimLeftTest.java

@@ -0,0 +1,55 @@
+package org.jabref.model.entry;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
+class BibEntryTrimLeftTest {
+
+    @Test
+    void trimLeftRemovesLeadingWhitespaceFromParsedSerializationAndComments() {
+        BibEntry entry = new BibEntry();
+        // include leading and trailing whitespace
+        entry.setParsedSerialization("  \t\n  Some serialization  \n\t  ");
+        entry.setCommentsBeforeEntry("   % a comment   \n");
+
+        // sanity
+        assertNotNull(entry.getParsedSerialization());
+        assertNotNull(entry.getUserComments());
+
+        entry.trimLeft();
+
+        // Current implementation uses String.trim(), which removes leading and trailing whitespace.
+        // The important bit to test here is that leading whitespace is gone.
+        assertEquals("Some serialization", entry.getParsedSerialization());
+        assertEquals("% a comment", entry.getUserComments());
+    }
+
+    @Test
+    void trimLeftIsIdempotent() {
+        BibEntry entry = new BibEntry();
+        entry.setParsedSerialization("   Text   ");
+        entry.setCommentsBeforeEntry("   % c   ");
+
+        entry.trimLeft();
+        String afterFirst = entry.getParsedSerialization();
+        String commentsAfterFirst = entry.getUserComments();
+
+        entry.trimLeft();
+        assertEquals(afterFirst, entry.getParsedSerialization());
+        assertEquals(commentsAfterFirst, entry.getUserComments());
+    }
+
+    @Test
+    void trimLeftWithEmptyStringsKeepsEmpty() {
+        BibEntry entry = new BibEntry();
+        entry.setParsedSerialization("");
+        entry.setCommentsBeforeEntry("");
+
+        entry.trimLeft();
+
+        assertEquals("", entry.getParsedSerialization());
+        assertEquals("", entry.getUserComments());
+    }
+}