Add ternary operator type inference tests

rust/src/analyzer/conditionals.rs

@@ -463,4 +463,76 @@ end
         let ret_vtx = info.return_vertex.unwrap();
         assert_eq!(get_type_show(&genv, ret_vtx), "String");
     }
+
+    // Test 11: ternary operator - different types → union
+    #[test]
+    fn test_ternary_union_type() {
+        let source = r#"
+class Foo
+  def bar
+    true ? "hello" : 42
+  end
+end
+"#;
+        let genv = analyze(source);
+        let info = genv
+            .resolve_method(&Type::instance("Foo"), "bar")
+            .expect("Foo#bar should be registered");
+        let ret_vtx = info.return_vertex.unwrap();
+        assert_eq!(get_type_show(&genv, ret_vtx), "(Integer | String)");
+    }
+
+    // Test 12: ternary operator - same type → single type
+    #[test]
+    fn test_ternary_same_type() {
+        let source = r#"
+class Foo
+  def bar
+    true ? "hello" : "world"
+  end
+end
+"#;
+        let genv = analyze(source);
+        let info = genv
+            .resolve_method(&Type::instance("Foo"), "bar")
+            .expect("Foo#bar should be registered");
+        let ret_vtx = info.return_vertex.unwrap();
+        assert_eq!(get_type_show(&genv, ret_vtx), "String");
+    }
+
+    // Test 13: ternary operator - nil branch → union with nil
+    #[test]
+    fn test_ternary_nil_branch() {
+        let source = r#"
+class Foo
+  def bar
+    true ? "hello" : nil
+  end
+end
+"#;
+        let genv = analyze(source);
+        let info = genv
+            .resolve_method(&Type::instance("Foo"), "bar")
+            .expect("Foo#bar should be registered");
+        let ret_vtx = info.return_vertex.unwrap();
+        assert_eq!(get_type_show(&genv, ret_vtx), "(String | nil)");
+    }
+
+    // Test 14: nested ternary operator
+    #[test]
+    fn test_ternary_nested() {
+        let source = r#"
+class Foo
+  def bar
+    true ? (false ? "inner" : 42) : :sym
+  end
+end
+"#;
+        let genv = analyze(source);
+        let info = genv
+            .resolve_method(&Type::instance("Foo"), "bar")
+            .expect("Foo#bar should be registered");
+        let ret_vtx = info.return_vertex.unwrap();
+        assert_eq!(get_type_show(&genv, ret_vtx), "(Integer | String | Symbol)");
+    }
 }

test/conditional_test.rb

@@ -215,4 +215,90 @@ def baz
 
     assert_check_error(source, method_name: 'upcase', receiver_type: 'Integer')
   end
+
+  # ============================================
+  # Ternary Operator - Type Inference
+  # ============================================
+
+  def test_ternary_union_type
+    source = <<~RUBY
+      x = true ? "hello" : 42
+    RUBY
+
+    types = infer(source)
+    assert_equal "(Integer | String)", types["x"]
+  end
+
+  def test_ternary_same_type
+    source = <<~RUBY
+      x = true ? "hello" : "world"
+    RUBY
+
+    assert_type source, "x", "String"
+  end
+
+  def test_ternary_nil_branch
+    source = <<~RUBY
+      x = true ? "hello" : nil
+    RUBY
+
+    types = infer(source)
+    assert_equal "(String | nil)", types["x"]
+  end
+
+  # ============================================
+  # Ternary Operator - No Error
+  # ============================================
+
+  def test_ternary_string_upcase
+    source = <<~RUBY
+      class Foo
+        def bar
+          true ? "a" : "b"
+        end
+
+        def baz
+          self.bar.upcase
+        end
+      end
+    RUBY
+
+    assert_no_check_errors(source)
+  end
+
+  # ============================================
+  # Ternary Operator - Error Detection
+  # ============================================
+
+  def test_ternary_string_even_error
+    source = <<~RUBY
+      class Foo
+        def bar
+          true ? "a" : "b"
+        end
+
+        def baz
+          self.bar.even?
+        end
+      end
+    RUBY
+
+    assert_check_error(source, method_name: 'even?', receiver_type: 'String')
+  end
+
+  def test_ternary_nested_error
+    source = <<~RUBY
+      class Foo
+        def bar
+          true ? (false ? "inner" : "other") : "fallback"
+        end
+
+        def baz
+          self.bar.even?
+        end
+      end
+    RUBY
+
+    assert_check_error(source, method_name: 'even?', receiver_type: 'String')
+  end
 end