add and extend unit tests

src/test/java/org/jabref/logic/formatter/bibtexfields/AddBracesFormatterTest.java

@@ -72,4 +72,9 @@ public void formatDoesNotRemoveBracesInBrokenString() {
     public void formatExample() {
         assertEquals("{In CDMA}", formatter.format(formatter.getExampleInput()));
     }
+
+    @Test
+    public void formatStringWithMinimalRequiredLength() {
+        assertEquals("{AB}", formatter.format("AB"));
+    }
 }

src/test/java/org/jabref/logic/formatter/bibtexfields/NormalizePagesFormatterTest.java

@@ -62,6 +62,7 @@ private static Stream<Arguments> tests() {
                 // special case, where -- is also put into
                 Arguments.of("some--text", "some-text"),
                 Arguments.of("pages 1--50", "pages 1-50"),
+                Arguments.of("--43", "-43"),
 
                 // keep arbitrary text
                 Arguments.of("some-text-with-dashes", "some-text-with-dashes"),

src/test/java/org/jabref/logic/integrity/ValidCitationKeyCheckerTest.java

@@ -0,0 +1,30 @@
+package org.jabref.logic.integrity;
+
+import java.util.Optional;
+import java.util.stream.Stream;
+
+import org.jabref.logic.l10n.Localization;
+
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class ValidCitationKeyCheckerTest {
+
+    private final ValidCitationKeyChecker checker = new ValidCitationKeyChecker();
+
+    @ParameterizedTest
+    @MethodSource("provideCitationKeys")
+    void citationKeyValidity(Optional optionalArgument, String citationKey, String errorMessage) {
+        assertEquals(optionalArgument, checker.checkValue(citationKey), errorMessage);
+    }
+
+    private static Stream<Arguments> provideCitationKeys() {
+        return Stream.of(
+                Arguments.of(Optional.of(Localization.lang("empty citation key")), "", "Citation key not empty"),
+                Arguments.of(Optional.empty(), "Seaver2019", "Invalid citation key"),
+                Arguments.of(Optional.of(Localization.lang("Invalid citation key")), "Seaver_2019}", "Valid citation key"));
+    }
+}