Add test for Pangram.java (#2986)

src/test/java/com/thealgorithms/strings/PangramTest.java

@@ -0,0 +1,24 @@
+package com.thealgorithms.strings;
+
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.*;
+
+
+public class PangramTest {
+    @Test
+    public void isPangram() {
+        String fullAlphabet = "abcdefghijklmnopqrstuvwxyz";
+        String notFullAlphabet = "abcdefghiklmnopqrstuvwxyz";
+        String fullMixedCaseAlphabet = "a BCDE fghIjkLMnop qrSTuv WXYz";
+        String sentence1 = "The quick brown fox jumps over the lazy dog";
+        String sentence2 = "The quick brown fox jumps over the lazy gentleman";  // missing letter d
+
+        assertTrue(Pangram.isPangram(fullAlphabet));
+        assertFalse(Pangram.isPangram(notFullAlphabet));
+        assertTrue(Pangram.isPangram(fullMixedCaseAlphabet));
+        assertTrue(Pangram.isPangram(sentence1));
+        assertFalse(Pangram.isPangram(sentence2));
+
+    }
+}