New AssertThatInstanceOf inspection that moves instanceof expressions out of assertThat(). Fixes to documentation.

src/test/java/de/platon42/intellij/playground/Playground.java

@@ -242,6 +242,13 @@ public class Playground {
         assertThat(opt).isAbsent();
     }
 
+    private void assertThatInstance() {
+        String foo = "foo";
+        assertThat(foo instanceof String).isTrue();
+        assertThat(foo).isInstanceOf(String.class);
+        assertThat(foo).isNotInstanceOf(String.class);
+    }
+
     private void junitAssertions() {
         assertFalse(!(new int[3].length == new ArrayList<Integer>().size()));
         assertThat(!(new int[3].length == new ArrayList<Integer>().size())).isFalse();

src/test/java/de/platon42/intellij/plugins/cajon/inspections/AssertThatInstanceOfInspectionTest.kt

@@ -0,0 +1,22 @@
+package de.platon42.intellij.plugins.cajon.inspections
+
+import com.intellij.testFramework.fixtures.JavaCodeInsightTestFixture
+import de.platon42.intellij.jupiter.MyFixture
+import de.platon42.intellij.jupiter.TestDataSubPath
+import de.platon42.intellij.plugins.cajon.AbstractCajonTest
+import org.junit.jupiter.api.Test
+
+internal class AssertThatInstanceOfInspectionTest : AbstractCajonTest() {
+
+    @Test
+    @TestDataSubPath("inspections/InstanceOf")
+    internal fun assertThat_with_instanceof_can_be_moved_out(@MyFixture myFixture: JavaCodeInsightTestFixture) {
+        runTest {
+            myFixture.enableInspections(AssertThatInstanceOfInspection::class.java)
+            myFixture.configureByFile("InstanceOfBefore.java")
+            executeQuickFixes(myFixture, Regex.fromLiteral("Replace instanceof expression by assertThat().isInstanceOf()"), 5)
+            executeQuickFixes(myFixture, Regex.fromLiteral("Replace instanceof expression by assertThat().isNotInstanceOf()"), 6)
+            myFixture.checkResultByFile("InstanceOfAfter.java")
+        }
+    }
+}

src/test/resources/inspections/InstanceOf/InstanceOfAfter.java

@@ -0,0 +1,22 @@
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class InstanceOf {
+
+    private void instanceOf() {
+        Boolean object = Boolean.TRUE;
+
+        assertThat(object).isInstanceOf(Boolean.class);
+        assertThat(object).isInstanceOf(Boolean.class);
+        assertThat(object).isInstanceOf(Boolean.class);
+        assertThat(object).isInstanceOf(Boolean.class);
+        assertThat(object).isInstanceOf(Boolean.class);
+
+        assertThat(object).isNotInstanceOf(Boolean.class);
+        assertThat(object).isNotInstanceOf(Boolean.class);
+        assertThat(object).isNotInstanceOf(Boolean.class);
+        assertThat(object).isNotInstanceOf(Boolean.class);
+        assertThat(object).isNotInstanceOf(Boolean.class);
+
+        assertThat(object).as("nah").isNotInstanceOf(Boolean.class);
+    }
+}

src/test/resources/inspections/InstanceOf/InstanceOfBefore.java

@@ -0,0 +1,22 @@
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class InstanceOf {
+
+    private void instanceOf() {
+        Boolean object = Boolean.TRUE;
+
+        assertThat(object instanceof Boolean).isEqualTo(Boolean.TRUE);
+        assertThat(object instanceof Boolean).isEqualTo(true);
+        assertThat(object instanceof Boolean).isNotEqualTo(Boolean.FALSE);
+        assertThat(object instanceof Boolean).isNotEqualTo(false);
+        assertThat(object instanceof Boolean).isTrue();
+
+        assertThat(object instanceof Boolean).isEqualTo(Boolean.FALSE);
+        assertThat(object instanceof Boolean).isEqualTo(false);
+        assertThat(object instanceof Boolean).isNotEqualTo(Boolean.TRUE);
+        assertThat(object instanceof Boolean).isNotEqualTo(true);
+        assertThat(object instanceof Boolean).isFalse();
+
+        assertThat(((object)) instanceof Boolean).as("nah").isEqualTo(true && !true);
+    }
+}