Add test cases for filter programming language feature

src/test/java/seedu/address/logic/commands/FilterProgrammingLanguageCommandTest.java

@@ -6,8 +6,13 @@
 import static seedu.address.logic.Messages.MESSAGE_PERSONS_LISTED_OVERVIEW;
 import static seedu.address.logic.commands.CommandTestUtil.assertCommandSuccess;
 import static seedu.address.logic.parser.FilterProgrammingLanguageCommandParser.createLanguages;
+import static seedu.address.testutil.TypicalPersons.ALICE;
+import static seedu.address.testutil.TypicalPersons.BENSON;
+import static seedu.address.testutil.TypicalPersons.CARL;
+import static seedu.address.testutil.TypicalPersons.DANIEL;
 import static seedu.address.testutil.TypicalPersons.getTypicalAddressBook;
 
+import java.util.Arrays;
 import java.util.Collections;
 
 import org.junit.jupiter.api.Test;
@@ -65,6 +70,28 @@ public void execute_zeroKeywords_noPersonFound() throws ParseException {
         assertCommandSuccess(command, model, expectedMessage, expectedModel);
         assertEquals(Collections.emptyList(), model.getFilteredPersonList());
     }
+
+    @Test
+    public void execute_multipleKeywords_multiplePersonsFound() throws ParseException {
+        String expectedMessage = String.format(MESSAGE_PERSONS_LISTED_OVERVIEW, 4);
+        ProgrammingLanguageContainsKeywordsPredicate predicate = preparePredicate("Java java");
+        FilterProgrammingLanguageCommand command = new FilterProgrammingLanguageCommand(predicate);
+        expectedModel.updateFilteredPersonList(predicate);
+        assertCommandSuccess(command, model, expectedMessage, expectedModel);
+        assertEquals(Arrays.asList(ALICE, BENSON, CARL, DANIEL), model.getFilteredPersonList());
+    }
+
+    @Test
+    public void toStringMethod() throws ParseException {
+        ProgrammingLanguageContainsKeywordsPredicate predicate = new ProgrammingLanguageContainsKeywordsPredicate(
+                createLanguages("Java"));
+        FilterProgrammingLanguageCommand filterProgrammingLanguageCommand =
+                new FilterProgrammingLanguageCommand(predicate);
+        String expected = FilterProgrammingLanguageCommand.class.getCanonicalName()
+                + "{programming_language=" + predicate + "}";
+        assertEquals(expected, filterProgrammingLanguageCommand.toString());
+    }
+
     /**
      * Parses {@code userInput} into a {@code ProgrammingLanguageContainsKeywordsPredicate}.
      */

src/test/java/seedu/address/logic/parser/FilterProgrammingLanguageCommandParserTest.java

@@ -0,0 +1,34 @@
+package seedu.address.logic.parser;
+
+import static seedu.address.logic.Messages.MESSAGE_INVALID_COMMAND_FORMAT;
+import static seedu.address.logic.parser.CommandParserTestUtil.assertParseFailure;
+import static seedu.address.logic.parser.CommandParserTestUtil.assertParseSuccess;
+import static seedu.address.logic.parser.FilterProgrammingLanguageCommandParser.createLanguages;
+
+import org.junit.jupiter.api.Test;
+
+import seedu.address.logic.commands.FilterProgrammingLanguageCommand;
+import seedu.address.logic.parser.exceptions.ParseException;
+import seedu.address.model.language.ProgrammingLanguageContainsKeywordsPredicate;
+
+public class FilterProgrammingLanguageCommandParserTest {
+    private FilterProgrammingLanguageCommandParser parser = new FilterProgrammingLanguageCommandParser();
+
+    @Test
+    public void parse_emptyArg_throwsParseException() {
+        assertParseFailure(parser, "     ", String.format(MESSAGE_INVALID_COMMAND_FORMAT,
+                FilterProgrammingLanguageCommand.MESSAGE_USAGE));
+    }
+
+    @Test
+    public void parse_validArgs_returnsFilterTagCommand() throws ParseException {
+        // no leading and trailing whitespaces
+        FilterProgrammingLanguageCommand expectedFilterProgrammingLanguageCommand =
+                new FilterProgrammingLanguageCommand(new ProgrammingLanguageContainsKeywordsPredicate(
+                        createLanguages("Java", "Python")));
+        assertParseSuccess(parser, "Java Python", expectedFilterProgrammingLanguageCommand);
+
+        // multiple whitespaces between keywords
+        assertParseSuccess(parser, " \n Java \n \t Python  \t", expectedFilterProgrammingLanguageCommand);
+    }
+}