Add first set of assertions

assertj-introduction/src/main/java/com/baeldung/assertj/domain/Dog.java

@@ -0,0 +1,19 @@
+package com.baeldung.assertj.domain;
+
+public class Dog {
+    private String name;
+    private Float weight;
+
+    public Dog(String name, Float weight) {
+        this.name = name;
+        this.weight = weight;
+    }
+
+    public String getName() {
+        return name;
+    }
+
+    public Float getWeight() {
+        return weight;
+    }
+}

assertj-introduction/src/test/java/com/baeldung/assertj/AssertJDemoTest.java

@@ -1,10 +1,65 @@
 package com.baeldung.assertj;
 
+import com.baeldung.assertj.domain.Dog;
 import org.junit.Test;
 
+import java.util.Arrays;
+import java.util.List;
+import java.util.NoSuchElementException;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.withPrecision;
+
 public class AssertJDemoTest {
 
     @Test
-    public void shouldTest() throws Exception {
+    public void whenComparingReferences_thenNotEqual() throws Exception {
+        Dog fido = new Dog("Fido", 5.15f);
+        Dog fidosClone = new Dog("Fido", 5.15f);
+
+        assertThat(fido).isNotEqualTo(fidosClone);
+    }
+
+    @Test
+    public void whenComparingFields_thenEqual() throws Exception {
+        Dog fido = new Dog("Fido", 5.15f);
+        Dog fidosClone = new Dog("Fido", 5.15f);
+
+        assertThat(fido).isEqualToComparingFieldByFieldRecursively(fidosClone);
+    }
+
+    @Test
+    public void whenCheckingForElement_thenContains() throws Exception {
+        List<String> list = Arrays.asList("1", "2", "3");
+
+        assertThat(list)
+                .contains("1");
+    }
+
+    @Test
+    public void whenCheckingForElement_thenMultipleAssertions() throws Exception {
+        List<String> list = Arrays.asList("1", "2", "3");
+
+        assertThat(list)
+                .isNotEmpty()
+                .contains("1")
+                .startsWith("1")
+                .doesNotContainNull()
+                .containsSequence("2", "3");
+    }
+
+    @Test
+    public void whenCheckingRunnable_thenIsInterface() throws Exception {
+        assertThat(Runnable.class).isInterface();
+    }
+
+    @Test
+    public void whenAssigningNSEExToException_thenIsAssignable() throws Exception {
+        assertThat(Exception.class).isAssignableFrom(NoSuchElementException.class);
+    }
+
+    @Test
+    public void whenComparingWithOffset_thenEquals() throws Exception {
+        assertThat(5.1).isEqualTo(5, withPrecision(1d));
     }
 }