Creating more unit tests for NumericFieldComparatorTest (#8604)

* Inserting two more tests cases at NumericFieldComparatorTest

* Fixing missing test

src/test/java/org/jabref/gui/util/comparator/NumericFieldComparatorTest.java

@@ -62,4 +62,15 @@ public void compareWithPlusString() {
     public void compareWordWithMinus() {
         assertEquals(-1, comparator.compare("-abc", "-5"));
     }
+
+    @Test
+    void compareNumericSignalWithoutNumberWithLenghtBiggerThanOne() {
+        assertEquals(2, comparator.compare("- ", "+ "));
+    }
+
+    @Test
+    void compareNumericSignalAfterNumber() {
+        assertEquals(-2, comparator.compare("5- ", "7+ "));
+    }
+
 }