Implemented AssertThatEnumerableIsEmptyInspection. Improved literal values by constant value calculation, more refactoring.

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

@@ -1,12 +1,26 @@
 package de.platon42.intellij.playground;
 
+import org.assertj.core.api.ListAssert;
+
 import java.util.ArrayList;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.junit.Assert.*;
 
 public class Playground {
 
     private void sizeOfList() {
+        assertThat("string").as("foo").hasSize(0);
+        assertThat(new StringBuilder()).as("bar").hasSize(0);
+        ListAssert<String> etc = assertThat(new ArrayList<String>()).as("etc");
+        etc.hasSize(0);
+        assertThat(new Long[1]).as("etc").hasSize(0);
+
+        assertThat("string").as("foo").isEmpty();
+        assertThat(new StringBuilder()).as("bar").isEmpty();
+        assertThat(new ArrayList<Long>()).as("etc").isEmpty();
+        assertThat(new Long[1]).as("etc").isEmpty();
+
         assertThat(new ArrayList<>().size()).isEqualTo(1);
     }
 
@@ -54,4 +68,15 @@ public class Playground {
         assertThat(foo).hasSize(0);
     }
 
+    private void junitAssertions() {
+        assertTrue(true);
+        assertTrue("message", true);
+        assertFalse(true);
+        assertFalse("message", true);
+        assertEquals(1L, 2L);
+        assertEquals("message", 1L, 2L);
+        assertNotEquals(1L, 2L);
+        assertNotEquals("message", 1L, 2L);
+    }
+
 }

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

@@ -0,0 +1,21 @@
+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 AssertThatEnumerableIsEmptyInspectionTest : AbstractCajonTest() {
+
+    @Test
+    @TestDataSubPath("inspections/EnumerableIsEmpty")
+    internal fun assertThat_with_hasSize_zero_can_use_isEmpty(@MyFixture myFixture: JavaCodeInsightTestFixture) {
+        runTest {
+            myFixture.enableInspections(AssertThatEnumerableIsEmptyInspection::class.java)
+            myFixture.configureByFile("EnumerableIsEmptyBefore.java")
+            executeQuickFixes(myFixture, Regex("Replace hasSize.*"), 4)
+            myFixture.checkResultByFile("EnumerableIsEmptyAfter.java")
+        }
+    }
+}

src/test/resources/inspections/EnumerableIsEmpty/EnumerableIsEmptyAfter.java

@@ -0,0 +1,18 @@
+import java.util.ArrayList;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class EnumerableIsEmpty {
+
+    private void enumerableIsEmpty() {
+        assertThat("string").as("foo").isEmpty();
+        assertThat(new StringBuilder()).as("bar").isEmpty();
+        assertThat(new ArrayList<Long>()).as("etc").isEmpty();
+        assertThat(new Long[1]).as("etc").isEmpty();
+
+        assertThat("string").as("foo").hasSize(1);
+        assertThat(new StringBuilder()).as("bar").hasSize(1);
+        assertThat(new ArrayList<Long>()).as("etc").hasSize(1);
+        assertThat(new Long[1]).as("etc").hasSize(1);
+    }
+}

src/test/resources/inspections/EnumerableIsEmpty/EnumerableIsEmptyBefore.java

@@ -0,0 +1,18 @@
+import java.util.ArrayList;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+public class EnumerableIsEmpty {
+
+    private void enumerableIsEmpty() {
+        assertThat("string").as("foo").hasSize(0);
+        assertThat(new StringBuilder()).as("bar").hasSize(0 + 0);
+        assertThat(new ArrayList<Long>()).as("etc").hasSize(10 / 100);
+        assertThat(new Long[1]).as("etc").hasSize(1 - 1);
+
+        assertThat("string").as("foo").hasSize(1);
+        assertThat(new StringBuilder()).as("bar").hasSize(1);
+        assertThat(new ArrayList<Long>()).as("etc").hasSize(1);
+        assertThat(new Long[1]).as("etc").hasSize(1);
+    }
+}

src/test/resources/inspections/StringIsEmpty/StringIsEmptyBefore.java

@@ -11,7 +11,7 @@ public class StringIsEmpty {
         assertThat(string).as("bar").hasSize(0);
 
         assertThat(stringBuilder).isEqualTo("foo");
-        assertThat(stringBuilder).as("foo").isEqualTo("");
+        assertThat(stringBuilder).as("foo").isEqualTo("" + "");
         assertThat(stringBuilder).as("bar").hasSize(0);
 
         assertThat(new Object()).isEqualTo("");