Add more unit tests

src/main/java/org/jabref/logic/bibtex/comparator/BibStringDiff.java

@@ -17,7 +17,7 @@ public class BibStringDiff {
     private final BibtexString originalString;
     private final BibtexString newString;
 
-    private BibStringDiff(BibtexString originalString, BibtexString newString) {
+    BibStringDiff(BibtexString originalString, BibtexString newString) {
         this.originalString = originalString;
         this.newString = newString;
     }
@@ -88,4 +88,22 @@ public BibtexString getOriginalString() {
     public BibtexString getNewString() {
         return newString;
     }
+
+    @Override
+    public boolean equals(Object other) {
+        if (this == other) {
+            return true;
+        }
+        if ((other == null) || (getClass() != other.getClass())) {
+            return false;
+        }
+
+        BibStringDiff that = (BibStringDiff) other;
+        return Objects.equals(newString, that.newString) && Objects.equals(originalString, that.originalString);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(originalString, newString);
+    }
 }

src/main/java/org/jabref/logic/bibtex/comparator/PreambleDiff.java

@@ -1,5 +1,6 @@
 package org.jabref.logic.bibtex.comparator;
 
+import java.util.Objects;
 import java.util.Optional;
 
 import org.jabref.model.database.BibDatabaseContext;
@@ -9,7 +10,7 @@ public class PreambleDiff {
     private final String originalPreamble;
     private final String newPreamble;
 
-    private PreambleDiff(String originalPreamble, String newPreamble) {
+    PreambleDiff(String originalPreamble, String newPreamble) {
         this.originalPreamble = originalPreamble;
         this.newPreamble = newPreamble;
     }
@@ -31,4 +32,22 @@ public String getNewPreamble() {
     public String getOriginalPreamble() {
         return originalPreamble;
     }
+
+    @Override
+    public boolean equals(Object other) {
+        if (this == other) {
+            return true;
+        }
+        if ((other == null) || (getClass() != other.getClass())) {
+            return false;
+        }
+
+        PreambleDiff that = (PreambleDiff) other;
+        return Objects.equals(newPreamble, that.newPreamble) && Objects.equals(originalPreamble, that.originalPreamble);
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(originalPreamble, newPreamble);
+    }
 }

src/main/java/org/jabref/model/entry/BibtexString.java

@@ -189,7 +189,6 @@ public boolean equals(Object o) {
         return (Objects.equals(hasChanged, that.hasChanged) &&
                 Objects.equals(name, that.name) &&
                 Objects.equals(content, that.content) &&
-                Objects.equals(id, that.id) &&
                 Objects.equals(type, that.type) &&
                 Objects.equals(parsedSerialization, that.parsedSerialization));
     }

src/test/java/org/jabref/logic/bibtex/comparator/BibStringDiffTest.java

@@ -0,0 +1,34 @@
+package org.jabref.logic.bibtex.comparator;
+
+import java.util.List;
+
+import org.jabref.model.database.BibDatabase;
+import org.jabref.model.entry.BibtexString;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class BibStringDiffTest {
+
+    private final BibDatabase originalDataBase = mock(BibDatabase.class);
+    private final BibDatabase newDataBase = mock(BibDatabase.class);
+    private final BibStringDiff diff = new BibStringDiff(new BibtexString("name2", "content2"), new BibtexString("name2", "content3"));
+
+    @BeforeEach
+    void setUp() {
+        when(originalDataBase.hasNoStrings()).thenReturn(false);
+        when(newDataBase.hasNoStrings()).thenReturn(false);
+        when(originalDataBase.getStringValues()).thenReturn(List.of(new BibtexString("name", "content"), new BibtexString("name2", "content2")));
+        when(newDataBase.getStringValues()).thenReturn(List.of(new BibtexString("name", "content"), new BibtexString("name2", "content3")));
+    }
+
+    @Test
+    void compareTest() {
+        BibStringDiff result = BibStringDiff.compare(originalDataBase, newDataBase).get(0);
+        assertEquals(diff, result);
+    }
+}

src/test/java/org/jabref/logic/bibtex/comparator/PreambleDiffTest.java

@@ -0,0 +1,45 @@
+package org.jabref.logic.bibtex.comparator;
+
+import java.util.Optional;
+
+import org.jabref.model.database.BibDatabase;
+import org.jabref.model.database.BibDatabaseContext;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.when;
+
+public class PreambleDiffTest {
+
+    private final BibDatabaseContext originalDataBaseContext = mock(BibDatabaseContext.class);
+    private final BibDatabaseContext newDataBaseContext = mock(BibDatabaseContext.class);
+    private final BibDatabase originalDataBase = mock(BibDatabase.class);
+    private final BibDatabase newDataBase = mock(BibDatabase.class);
+
+    @BeforeEach
+    void setUp() {
+        when(originalDataBaseContext.getDatabase()).thenReturn(originalDataBase);
+        when(newDataBaseContext.getDatabase()).thenReturn(newDataBase);
+    }
+
+    @Test
+    void compareSamePreambleTest() {
+        when(originalDataBase.getPreamble()).thenReturn(Optional.of("preamble"));
+        when(newDataBase.getPreamble()).thenReturn(Optional.of("preamble"));
+
+        assertEquals(Optional.empty(), PreambleDiff.compare(originalDataBaseContext, newDataBaseContext));
+    }
+
+    @Test
+    void compareDifferentPreambleTest() {
+        when(originalDataBase.getPreamble()).thenReturn(Optional.of("preamble"));
+        when(newDataBase.getPreamble()).thenReturn(Optional.of("otherPreamble"));
+
+        PreambleDiff expected = new PreambleDiff("preamble", "otherPreamble");
+        PreambleDiff result = PreambleDiff.compare(originalDataBaseContext, newDataBaseContext).orElse(null);
+        assertEquals(expected, result);
+    }
+}