Avoid private imports in test cases. (#3403)

tests/test_content.py

@@ -4,7 +4,6 @@
 import pytest
 
 import httpx
-from httpx._content import encode_json
 
 method = "POST"
 url = "https://www.example.com"
@@ -489,24 +488,20 @@ def test_response_invalid_argument():
 
 def test_ensure_ascii_false_with_french_characters():
     data = {"greeting": "Bonjour, ça va ?"}
-    headers, byte_stream = encode_json(data)
-    json_output = b"".join(byte_stream).decode("utf-8")
-
+    response = httpx.Response(200, json=data)
     assert (
-        "ça va" in json_output
+        "ça va" in response.text
     ), "ensure_ascii=False should preserve French accented characters"
-    assert headers["Content-Type"] == "application/json"
+    assert response.headers["Content-Type"] == "application/json"
 
 
 def test_separators_for_compact_json():
     data = {"clé": "valeur", "liste": [1, 2, 3]}
-    headers, byte_stream = encode_json(data)
-    json_output = b"".join(byte_stream).decode("utf-8")
-
+    response = httpx.Response(200, json=data)
     assert (
-        json_output == '{"clé":"valeur","liste":[1,2,3]}'
+        response.text == '{"clé":"valeur","liste":[1,2,3]}'
     ), "separators=(',', ':') should produce a compact representation"
-    assert headers["Content-Type"] == "application/json"
+    assert response.headers["Content-Type"] == "application/json"
 
 
 def test_allow_nan_false():
@@ -516,8 +511,8 @@ def test_allow_nan_false():
     with pytest.raises(
         ValueError, match="Out of range float values are not JSON compliant"
     ):
-        encode_json(data_with_nan)
+        httpx.Response(200, json=data_with_nan)
     with pytest.raises(
         ValueError, match="Out of range float values are not JSON compliant"
     ):
-        encode_json(data_with_inf)
+        httpx.Response(200, json=data_with_inf)