test: added isNumber test

src/test/java/org/example/AdministrationTest.java

@@ -20,4 +20,27 @@ class AdministrationTest {
 
 
     }
+
+    @Test
+    void isNumber() {
+
+        Administration administration = new Administration();
+        String full01 = "S1002";
+        String str1 = full01.substring(1);
+        String full02 = "S100Z";
+        String str2 = full02.substring(1);
+        String full03 = "P1004";
+        String str3 = full03.substring(1);
+
+
+        boolean test01 = administration.isNumber(str1);
+        boolean test02 = administration.isNumber(str2);
+        boolean test03 = administration.isNumber(str3);
+
+        assertEquals(true, test01);
+        assertEquals(false, test02);
+        assertEquals(true, test03);
+
+    }
+
 }