test(core): cover ChangeSetStack scopes (#31)

Fixes #21

Adds focused unit coverage for nested change-set scopes, precedence, clearing, and pop fallback.

Author: philipgreat

teaql-core/src/test/java/io/teaql/core/ChangeSetStackTest.java

@@ -0,0 +1,105 @@
+package io.teaql.core;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNotSame;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+
+import java.util.Set;
+import org.junit.Test;
+
+public class ChangeSetStackTest {
+
+    private static final EntityKey ORDER = new EntityKey("Order", 1L);
+    private static final EntityKey OTHER_ORDER = new EntityKey("Order", 2L);
+
+    @Test
+    public void emptyStackHasNoCurrentOrPoppedChangeSet() {
+        ChangeSetStack stack = new ChangeSetStack();
+
+        assertNull(stack.current());
+        assertNull(stack.pop());
+    }
+
+    @Test
+    public void firstSetLazilyCreatesCurrentChangeSet() {
+        ChangeSetStack stack = new ChangeSetStack();
+
+        stack.set(ORDER, "status", "CREATED");
+
+        assertNotNull(stack.current());
+        assertEquals("CREATED", stack.current().get(ORDER, "status"));
+    }
+
+    @Test
+    public void topScopeShadowsLowerScopeAndPopRestoresIt() {
+        ChangeSetStack stack = new ChangeSetStack();
+        stack.set(ORDER, "status", "CREATED");
+        stack.push();
+        stack.set(ORDER, "status", "PAID");
+
+        assertEquals("PAID", stack.get(ORDER, "status"));
+
+        EntityChangeSet popped = stack.pop();
+
+        assertEquals("PAID", popped.get(ORDER, "status"));
+        assertEquals("CREATED", stack.get(ORDER, "status"));
+    }
+
+    @Test
+    public void clearCurrentClearsOnlyTopScope() {
+        ChangeSetStack stack = new ChangeSetStack();
+        stack.set(ORDER, "status", "CREATED");
+        stack.push();
+        EntityChangeSet top = stack.current();
+        stack.set(ORDER, "status", "PAID");
+
+        stack.clearCurrent();
+
+        assertEquals("CREATED", stack.get(ORDER, "status"));
+        assertTrue(stack.current().isEmpty());
+        assertNotSame(top, stack.current());
+    }
+
+    @Test
+    public void changedFieldNamesAreCombinedAcrossScopes() {
+        ChangeSetStack stack = new ChangeSetStack();
+        stack.set(ORDER, "status", "CREATED");
+        stack.push();
+        stack.set(ORDER, "total", 100L);
+        stack.set(OTHER_ORDER, "comment", "other");
+
+        assertEquals(Set.of("status", "total"), stack.changedFieldNames(ORDER));
+        assertEquals(Set.of("comment"), stack.changedFieldNames(OTHER_ORDER));
+    }
+
+    @Test
+    public void clearEntityRemovesItFromEveryScopeOnly() {
+        ChangeSetStack stack = new ChangeSetStack();
+        stack.set(ORDER, "status", "CREATED");
+        stack.set(OTHER_ORDER, "status", "CREATED");
+        stack.push();
+        stack.set(ORDER, "total", 100L);
+        stack.set(OTHER_ORDER, "total", 200L);
+
+        stack.clearEntity(ORDER);
+
+        assertNull(stack.get(ORDER, "status"));
+        assertNull(stack.get(ORDER, "total"));
+        assertEquals("CREATED", stack.get(OTHER_ORDER, "status"));
+        assertEquals(200L, stack.get(OTHER_ORDER, "total"));
+    }
+
+    @Test
+    public void pushCreatesASeparateCurrentChangeSet() {
+        ChangeSetStack stack = new ChangeSetStack();
+        EntityChangeSet first = stack.currentMut();
+
+        stack.push();
+
+        assertSame(stack.current(), stack.currentMut());
+        assertNotSame(first, stack.current());
+    }
+}