Reduced minimal supported IDEA version from 2018.2 to 2017.2.

Added AssertThatGuavaOptional inspection. Prepared next release.
Bumped to Kotlin 1.3.30.

src/test/resources/inspections/AssertThatGuavaOptional/AssertThatGuavaOptionalAfter.java

@@ -0,0 +1,36 @@
+import com.google.common.base.Optional;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.guava.api.Assertions.assertThat;
+
+public class AssertThatGuavaOptional {
+
+    private void assertThatGuavaOptional() {
+        Optional<String> opt = Optional.absent();
+
+        assertThat(opt).isPresent();
+        assertThat(opt).isPresent();
+        assertThat(opt).isPresent();
+        assertThat(opt).isPresent();
+        assertThat(opt).isPresent();
+
+        assertThat(opt).isAbsent();
+        assertThat(opt).isAbsent();
+        assertThat(opt).isAbsent();
+        assertThat(opt).isAbsent();
+        assertThat(opt).isAbsent();
+
+        assertThat(opt).contains("foo");
+        assertThat(opt.get()).isSameAs("foo");
+        assertThat(opt.get()).isNotEqualTo("foo");
+        assertThat(opt.get()).isNotSameAs("foo");
+
+        assertThat(opt).contains("foo");
+        assertThat(opt).contains("foo");
+        assertThat(opt).isNotEqualTo(Optional.of("foo"));
+        assertThat(opt).isNotEqualTo(Optional.fromNullable("foo"));
+
+        assertThat(opt).isAbsent();
+        assertThat(opt).isPresent();
+    }
+}

src/test/resources/inspections/AssertThatGuavaOptional/AssertThatGuavaOptionalBefore.java

@@ -0,0 +1,36 @@
+import com.google.common.base.Optional;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.guava.api.Assertions.assertThat;
+
+public class AssertThatGuavaOptional {
+
+    private void assertThatGuavaOptional() {
+        Optional<String> opt = Optional.absent();
+
+        assertThat(opt.isPresent()).isEqualTo(true);
+        assertThat(opt.isPresent()).isEqualTo(Boolean.TRUE);
+        assertThat(opt.isPresent()).isNotEqualTo(false);
+        assertThat(opt.isPresent()).isNotEqualTo(Boolean.FALSE);
+        assertThat(opt.isPresent()).isTrue();
+
+        assertThat(opt.isPresent()).isEqualTo(false);
+        assertThat(opt.isPresent()).isEqualTo(Boolean.FALSE);
+        assertThat(opt.isPresent()).isNotEqualTo(true);
+        assertThat(opt.isPresent()).isNotEqualTo(Boolean.TRUE);
+        assertThat(opt.isPresent()).isFalse();
+
+        assertThat(opt.get()).isEqualTo("foo");
+        assertThat(opt.get()).isSameAs("foo");
+        assertThat(opt.get()).isNotEqualTo("foo");
+        assertThat(opt.get()).isNotSameAs("foo");
+
+        assertThat(opt).isEqualTo(Optional.of("foo"));
+        assertThat(opt).isEqualTo(Optional.fromNullable("foo"));
+        assertThat(opt).isNotEqualTo(Optional.of("foo"));
+        assertThat(opt).isNotEqualTo(Optional.fromNullable("foo"));
+
+        assertThat(opt).isEqualTo(Optional.absent());
+        assertThat(opt).isNotEqualTo(Optional.absent());
+    }
+}