ComplexTest made

Closes #25

src/test/java/edu/ntnu/idatt2003/model/ComplexTest.java

+package edu.ntnu.idatt2003.model;
+
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Nested;
+import org.junit.jupiter.api.Test;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+public class ComplexTest {
+  private Complex complex;
+
+  @BeforeEach
+  public void setUp() {
+    complex = new Complex(1, 2);
+  }
+
+  @Nested
+  @DisplayName("Positive tests for the Complex class.")
+  class PositiveComplexTest {
+    @Test
+    void testSqrt() {
+      Complex result = complex.sqrt();
+      assertEquals(1.272, result.getX0(), 0.001);
+      assertEquals(0.786, result.getX1(), 0.001);
+    }
+  }
+}