add test_save_load_dragonnet

tests/test_dragon.py

@@ -0,0 +1,18 @@
+from causalml.inference.tf import DragonNet
+from causalml.dataset.regression import *
+import shutil
+
+
+def test_save_load_dragonnet():
+    y, X, w, tau, b, e = simulate_nuisance_and_easy_treatment(n=1000)
+
+    dragon = DragonNet(neurons_per_layer=200, targeted_reg=True, verbose=False)
+    dragon_ite = dragon.fit_predict(X, w, y, return_components=False)
+    dragon_ate = dragon_ite.mean()
+    dragon.save("smaug")
+
+    smaug = DragonNet()
+    smaug.load("smaug")
+    shutil.rmtree("smaug")
+
+    assert smaug.predict_tau(X).mean() == dragon_ate