test(workflow): erp-workflow 单元测试从 16 增至 63 — 覆盖 model/error/parser/expression/executor

- model.rs: 13 个 FlowGraph 测试（build/outgoing/incoming/start-end 边界）
- error.rs: 7 个 WorkflowError → AppError 转换测试
- parser.rs: 11 个新增验证边界测试（空图/多起点/幽灵边/网关约束）
- expression.rs: 13 个新增求值测试（float/bool/string/复合表达式/空白容错）
- executor.rs: 3 个 is_join_gateway 纯函数测试

crates/erp-workflow/src/engine/expression.rs

@@ -328,4 +328,105 @@ mod tests {
         let result = ExpressionEvaluator::eval("justavariable", &vars);
         assert!(result.is_err());
     }
+
+    // ---- 扩展边界测试 ----
+
+    #[test]
+    fn test_less_or_equal() {
+        let vars = make_vars();
+        assert!(ExpressionEvaluator::eval("amount <= 1500", &vars).unwrap());
+        assert!(ExpressionEvaluator::eval("amount <= 2000", &vars).unwrap());
+        assert!(!ExpressionEvaluator::eval("amount <= 1000", &vars).unwrap());
+    }
+
+    #[test]
+    fn test_boolean_equality() {
+        let vars = make_vars();
+        assert!(ExpressionEvaluator::eval("active == true", &vars).unwrap());
+        assert!(!ExpressionEvaluator::eval("active == false", &vars).unwrap());
+    }
+
+    #[test]
+    fn test_string_literal_with_single_quotes() {
+        let vars = make_vars();
+        assert!(ExpressionEvaluator::eval("status == 'approved'", &vars).unwrap());
+    }
+
+    #[test]
+    fn test_float_comparison() {
+        let mut vars = HashMap::new();
+        vars.insert("temperature".to_string(), json!(36.5));
+        assert!(ExpressionEvaluator::eval("temperature >= 36.0", &vars).unwrap());
+        assert!(ExpressionEvaluator::eval("temperature < 37.0", &vars).unwrap());
+        assert!(!ExpressionEvaluator::eval("temperature > 37.5", &vars).unwrap());
+    }
+
+    #[test]
+    fn test_integer_float_cross_comparison() {
+        let mut vars = HashMap::new();
+        vars.insert("val".to_string(), json!(10));
+        assert!(ExpressionEvaluator::eval("val == 10.0", &vars).unwrap());
+        assert!(ExpressionEvaluator::eval("val >= 9.5", &vars).unwrap());
+    }
+
+    #[test]
+    fn test_string_comparison_lexicographic() {
+        let vars = make_vars();
+        // name = "Alice"
+        assert!(!ExpressionEvaluator::eval("name > \"Alice\"", &vars).unwrap());
+        assert!(ExpressionEvaluator::eval("name >= \"Alice\"", &vars).unwrap());
+        assert!(ExpressionEvaluator::eval("name < \"Bob\"", &vars).unwrap());
+        assert!(ExpressionEvaluator::eval("name == \"Alice\"", &vars).unwrap());
+    }
+
+    #[test]
+    fn test_compound_and_or() {
+        let vars = make_vars();
+        // amount > 1000 (true) && score > 80 (true) || amount > 3000 (false)
+        // OR 先绑定，所以是 amount>1000 && score>80 (true) || amount>3000 (false)
+        // 注意：当前实现从左到右先匹配 ||，所以实际解析为:
+        // amount > 1000 && score > 80 || amount > 3000
+        // find_logical_op 先找 || → split at ||
+        // left = "amount > 1000 && score > 80", right = "amount > 3000"
+        // left = true, right = false → true || false = true
+        assert!(ExpressionEvaluator::eval(
+            "amount > 1000 && score > 80 || amount > 3000", &vars
+        ).unwrap());
+    }
+
+    #[test]
+    fn test_compound_all_false() {
+        let vars = make_vars();
+        assert!(!ExpressionEvaluator::eval(
+            "amount > 2000 && score > 90", &vars
+        ).unwrap());
+    }
+
+    #[test]
+    fn test_number_not_equals() {
+        let vars = make_vars();
+        assert!(ExpressionEvaluator::eval("amount != 1000", &vars).unwrap());
+        assert!(!ExpressionEvaluator::eval("amount != 1500", &vars).unwrap());
+    }
+
+    #[test]
+    fn test_expression_with_extra_whitespace() {
+        let vars = make_vars();
+        assert!(ExpressionEvaluator::eval("  amount  >  1000  ", &vars).unwrap());
+    }
+
+    #[test]
+    fn test_unresolvable_variable_returns_error() {
+        let vars = HashMap::new();
+        let result = ExpressionEvaluator::eval("missing_var > 10", &vars);
+        assert!(result.is_err());
+        assert!(result.unwrap_err().to_string().contains("未知的变量"));
+    }
+
+    #[test]
+    fn test_empty_expression_returns_error() {
+        let vars = HashMap::new();
+        let result = ExpressionEvaluator::eval("", &vars);
+        assert!(result.is_err());
+    }
 }