Add some tests for language elements (#32)

* Add test for method mechanisms
* Add test for enumerations
* Add test for packages in Java
* Add test for optional

Author: mperor

FirstSteps/src/test/java/pl/mperor/lab/java/lang/element/EnumTest.java

@@ -0,0 +1,55 @@
+package pl.mperor.lab.java.lang.element;
+
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+
+public class EnumTest {
+
+    @Test
+    public void testEnumeration() {
+        Assertions.assertEquals(0, Season.SPRING.ordinal());
+        var hottestSeasons = Season.SUMMER;
+        Assertions.assertTrue(hottestSeasons == Season.SUMMER);
+        Assertions.assertEquals("FALL", Season.FALL.name());
+        Assertions.assertEquals(Season.WINTER, Season.valueOf("WINTER"));
+        Assertions.assertArrayEquals(new Month[]{Month.DECEMBER, Month.JANUARY, Month.FEBRUARY},
+                Season.WINTER.getMonths());
+        Assertions.assertEquals(4, Season.values().length);
+    }
+
+    enum Season {
+        SPRING(Month.MARCH, Month.APRIL, Month.MAY),
+        SUMMER(Month.JUNE, Month.JULY, Month.AUGUST),
+        FALL(Month.SEPTEMBER, Month.OCTOBER, Month.NOVEMBER),
+        WINTER(Month.DECEMBER, Month.JANUARY, Month.FEBRUARY);
+
+        private final Month[] months;
+
+        Season(Month... months) {
+            this.months = months;
+        }
+
+        Month[] getMonths() {
+            return Arrays.copyOf(months, months.length);
+        }
+    }
+
+    enum Month {
+        JANUARY,
+        FEBRUARY,
+        MARCH,
+        APRIL,
+        MAY,
+        JUNE,
+        JULY,
+        AUGUST,
+        SEPTEMBER,
+        OCTOBER,
+        NOVEMBER,
+        DECEMBER
+    }
+
+}

FirstSteps/src/test/java/pl/mperor/lab/java/lang/element/MethodTest.java

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+package pl.mperor.lab.java.lang.element;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+
+public class MethodTest {
+
+    @Test
+    public void testOverloading() {
+        byte b = 1;
+        Assertions.assertEquals(1, Overloading.countArgs(b), "Type Promotion");
+        Assertions.assertEquals(1, Overloading.countArgs(1.0), "Different Parameter Types");
+        Assertions.assertEquals(2, Overloading.countArgs(1, 'a'), "Different Number of Parameters");
+        Assertions.assertEquals(3, Overloading.countArgs("one", "two", "three"), "Varargs");
+        Assertions.assertEquals(0, Overloading.countArgs(), "Varargs");
+        Assertions.assertEquals(1, new Overloading().countArgs('c'), "Not only static!");
+    }
+
+    static class Overloading {
+        static int countArgs(long l) {
+            return 1;
+        }
+
+        static int countArgs(double d) {
+            return 1;
+        }
+
+        static <T> int countArgs(long l, T t) {
+            return 2;
+        }
+
+        static <T> int countArgs(T... t) {
+            return t != null ? t.length : 0;
+        }
+
+        int countArgs(char c) {
+            return 1;
+        }
+    }
+
+    @Test
+    public void testParameterPassingMechanism() {
+        int primitive = 0;
+        ParameterPassing.primitiveByValue(primitive);
+        Assertions.assertEquals(0, primitive);
+
+        String string = "original";
+        ParameterPassing.immutableObjectByValue(string);
+        Assertions.assertEquals("original", string);
+
+        int[] array = {1, 2, 3};
+        ParameterPassing.mutableObjectByValue(array);
+        Assertions.assertArrayEquals(new int[]{0, 0, 0}, array);
+    }
+
+    static class ParameterPassing {
+        static void primitiveByValue(int primitive) {
+            primitive = 1;
+        }
+
+        static void immutableObjectByValue(String immutable) {
+            immutable = "";
+        }
+
+        static void mutableObjectByValue(int[] array) {
+            Arrays.fill(array, 0);
+        }
+    }
+
+}

FirstSteps/src/test/java/pl/mperor/lab/java/lang/element/OptionalTest.java

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+package pl.mperor.lab.java.lang.element;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Optional;
+
+public class OptionalTest {
+
+    @Test
+    public void testOptionalImperatively() {
+        Assertions.assertFalse(SomeAPI.getNameById(0).isPresent());
+        // Please for(get), do not use get, instead use orElseThrow() / orElse("default")
+        Assertions.assertEquals("default", SomeAPI.getNameById(0).orElse("default"));
+        Assertions.assertEquals("some name", SomeAPI.getNameById(1).orElseThrow());
+    }
+
+    @Test
+    public void testOptionalFunctionally() {
+        SomeAPI.getNameById(1).ifPresentOrElse(
+                name -> Assertions.assertEquals("some name", name),
+                () -> Assertions.fail()
+        );
+    }
+
+    static class SomeAPI {
+
+        // 1. Return a reference if the value will always exist
+        // 2. Return an Optional<T> if the value may or may not exist
+        public static Optional<String> getNameById(long id) {
+            if (id == 0) {
+                return Optional.empty();
+            }
+
+            return Optional.of("some name");
+        }
+
+        // 3. Do not use Optional<T> for fields - overhead with little benefit
+        private String config;
+
+        // 4. Do not user Optional<T> for method parameters - user overloading instead
+        public void setConfig(String config) {
+            this.config = config;
+        }
+
+        public void setConfig() {
+            setConfig("default");
+        }
+    }
+
+}

FirstSteps/src/test/java/pl/mperor/lab/java/lang/element/PackageTest.java

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+package pl.mperor.lab.java.lang.element;
+
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+import java.util.Arrays;
+import java.util.stream.Collectors;
+
+public class PackageTest {
+
+    @Test
+    public void testPackage() {
+        Assertions.assertEquals("pl.mperor.lab.java.lang.element",
+                PackageTest.class.getPackageName(),
+                "Package is a box for classes");
+
+        Assertions.assertEquals("pl.mperor.lab.java.lang.element.PackageTest",
+                PackageTest.class.getName(),
+                "Package + class name => unique address");
+
+        Assertions.assertEquals("pl.mperor",
+                Arrays.stream("mperor.pl".split("\\."))
+                        .sorted((_, _) -> -1)
+                        .collect(Collectors.joining(".")),
+                "Packages use the reversed domain name");
+    }
+}