Add DEDUCTION-based polymorphism base tests for YAML to try to repro #…

…404

yaml/src/test/java/com/fasterxml/jackson/dataformat/yaml/misc/TestPolymorphicDeduction.java

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+package com.fasterxml.jackson.dataformat.yaml.misc;
+
+import com.fasterxml.jackson.annotation.JsonSubTypes;
+import com.fasterxml.jackson.annotation.JsonTypeInfo;
+
+import com.fasterxml.jackson.databind.*;
+import com.fasterxml.jackson.dataformat.yaml.ModuleTestBase;
+
+import static com.fasterxml.jackson.annotation.JsonSubTypes.Type;
+import static com.fasterxml.jackson.annotation.JsonTypeInfo.Id.DEDUCTION;
+
+// for [databind#43], deduction-based polymorphism
+public class TestPolymorphicDeduction extends ModuleTestBase
+{
+  @JsonTypeInfo(use = DEDUCTION)
+  @JsonSubTypes( {@Type(LiveCat.class), @Type(DeadCat.class), @Type(Fleabag.class)})
+  // A general supertype with no properties - used for tests involving {}
+  interface Feline {}
+
+  @JsonTypeInfo(use = DEDUCTION)
+  @JsonSubTypes( {@Type(LiveCat.class), @Type(DeadCat.class)})
+  // A supertype containing common properties
+  public static class Cat implements Feline {
+    public String name;
+  }
+
+  // Distinguished by its parent and a unique property
+  static class DeadCat extends Cat {
+    public String causeOfDeath;
+  }
+
+  // Distinguished by its parent and a unique property
+  static class LiveCat extends Cat {
+    public boolean angry;
+  }
+
+  // No distinguishing properties whatsoever
+  static class Fleabag implements Feline {
+    // NO OP
+  }
+
+  /*
+  /**********************************************************
+  /* Mock data
+  /**********************************************************
+   */
+
+  private static final String DEAD_CAT_DOC = "name: Felix\ncauseOfDeath: entropy\n";
+  private static final String LIVE_CAT_DOC = "name: Felix\nangry: true\n";
+
+  /*
+  /**********************************************************
+  /* Test methods
+  /**********************************************************
+   */
+
+  private final ObjectMapper MAPPER = newObjectMapper();
+
+  public void testSimpleInference() throws Exception
+  {
+    Cat cat = MAPPER.readValue(LIVE_CAT_DOC, Cat.class);
+    assertTrue(cat instanceof LiveCat);
+    assertSame(cat.getClass(), LiveCat.class);
+    assertEquals("Felix", cat.name);
+    assertTrue(((LiveCat)cat).angry);
+
+    cat = MAPPER.readValue(DEAD_CAT_DOC, Cat.class);
+    assertTrue(cat instanceof DeadCat);
+    assertSame(cat.getClass(), DeadCat.class);
+    assertEquals("Felix", cat.name);
+    assertEquals("entropy", ((DeadCat)cat).causeOfDeath);
+  }
+
+  public void testSimpleInferenceOfEmptySubtypeDoesntMatchNull() throws Exception {
+    Feline feline = MAPPER.readValue("null", Feline.class);
+    assertNull(feline);
+  }
+
+  public void testCaseInsensitiveInference() throws Exception
+  {
+    Cat cat = mapperBuilder()
+      .configure(MapperFeature.ACCEPT_CASE_INSENSITIVE_PROPERTIES, true)
+      .build()
+      .readValue(DEAD_CAT_DOC.toUpperCase(), Cat.class);
+    assertTrue(cat instanceof DeadCat);
+    assertSame(cat.getClass(), DeadCat.class);
+    assertEquals("FELIX", cat.name);
+    assertEquals("ENTROPY", ((DeadCat)cat).causeOfDeath);
+  }
+}