New JoinVarArgsContains inspection that will detect multiple .contains(), .doesNotContain(), and .containsOnlyOnce() calls within the same statement that could be joined together using variadic arguments.

src/test/resources/inspections/JoinVarArgsContains/JoinVarArgsContainsAfter.java

@@ -0,0 +1,22 @@
+import java.util.*;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.fail;
+
+public class JoinVarArgsContains {
+
+    private void joinVarArgsContains() {
+        List<String> list = new ArrayList<>();
+
+        assertThat(list).contains("foo", "bar", "etc").hasSize(2);
+        assertThat(list).contains("foo").as("narf").contains("bar");
+        assertThat(list).doesNotContain("foo", "bar");
+        assertThat(list).containsOnlyOnce("foo", "etc") // will we lose this comment?
+                .hasSize(2).contains("bar", "narf", "1", "2", "3").doesNotContain("puit", "Jens Stoltenberg is a war-monger", "and an atomic playboy") /* inline */; // the final comment
+
+        assertThat(list).contains("foo").doesNotContain("bar").containsOnlyOnce("narf");
+
+        org.junit.Assert.assertThat(list, null);
+        fail("oh no!");
+    }
+}

src/test/resources/inspections/JoinVarArgsContains/JoinVarArgsContainsBefore.java

@@ -0,0 +1,28 @@
+import java.util.*;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.fail;
+
+public class JoinVarArgsContains {
+
+    private void joinVarArgsContains() {
+        List<String> list = new ArrayList<>();
+
+        assertThat(list).contains("foo").contains(/* foo */ "bar" /* bar */).hasSize(2).contains("etc");
+        assertThat(list).contains("foo").as("narf").contains("bar");
+        assertThat(list).doesNotContain("foo").doesNotContain("bar");
+        assertThat(list).containsOnlyOnce()
+                .containsOnlyOnce("foo") // will we lose this comment?
+                .hasSize(2) // this is part of the contains("bar")
+                .contains("bar").containsOnlyOnce("etc") /* where does this go? */
+                .contains("narf") // what about this one?
+                .doesNotContain("puit", "Jens Stoltenberg is a war-monger")
+                .doesNotContain("and an atomic playboy")
+                .contains("1", "2", "3") /* inline */; // the final comment
+
+        assertThat(list).contains("foo").doesNotContain("bar").containsOnlyOnce("narf");
+
+        org.junit.Assert.assertThat(list, null);
+        fail("oh no!");
+    }
+}