diff --git a/json/circe/src/test/scala/sttp/client4/circe/CirceTests.scala b/json/circe/src/test/scala/sttp/client4/circe/CirceTests.scala
index bae5cf0bcb..26ca9d7dd5 100644
--- a/json/circe/src/test/scala/sttp/client4/circe/CirceTests.scala
+++ b/json/circe/src/test/scala/sttp/client4/circe/CirceTests.scala
@@ -107,11 +107,13 @@ class CirceTests extends AnyFlatSpec with Matchers with EitherValues {
     import sttp.model.Uri
 
     val jObject: JsonObject = JsonObject(("location", "hometown".asJson), ("bio", "Scala programmer".asJson))
-    val result = basicRequest.get(Uri("http://example.org")).body(jObject).body.show
+    val request = basicRequest.get(Uri("http://example.org")).body(jObject)
 
-    val expectedResult = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedBody = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedContentType = Some("application/json; charset=utf-8")
 
-    result should be(expectedResult)
+    request.contentType should be(expectedContentType)
+    request.body.show should be(expectedBody)
   }
 
   case class Inner(a: Int, b: Boolean, c: String)
diff --git a/json/json4s/src/test/scala/sttp/client4/Json4sTests.scala b/json/json4s/src/test/scala/sttp/client4/Json4sTests.scala
index a725c5f051..85642dd821 100644
--- a/json/json4s/src/test/scala/sttp/client4/Json4sTests.scala
+++ b/json/json4s/src/test/scala/sttp/client4/Json4sTests.scala
@@ -83,11 +83,13 @@ class Json4sTests extends AnyFlatSpec with Matchers with EitherValues {
 
   it should "serialize from JObject using implicit json4sBodySerializer" in {
     val jObject: JObject = JObject(JField("location", JString("hometown")), JField("bio", JString("Scala programmer")))
-    val result = basicRequest.get(Uri("http://example.org")).body(jObject).body.show
+    val request = basicRequest.get(Uri("http://example.org")).body(jObject)
 
-    val expectedResult = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedBody = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedContentType = Some("application/json; charset=utf-8")
 
-    result should be(expectedResult)
+    request.contentType should be(expectedContentType)
+    request.body.show should be(expectedBody)
   }
 
   def extractBody[T](request: PartialRequest[T]): String =
diff --git a/json/jsoniter/src/test/scala/sttp/client4/jsoniter/JsoniterJsonTests.scala b/json/jsoniter/src/test/scala/sttp/client4/jsoniter/JsoniterJsonTests.scala
index 26b037b65a..127d839cdf 100644
--- a/json/jsoniter/src/test/scala/sttp/client4/jsoniter/JsoniterJsonTests.scala
+++ b/json/jsoniter/src/test/scala/sttp/client4/jsoniter/JsoniterJsonTests.scala
@@ -83,11 +83,13 @@ class JsoniterJsonTests extends AnyFlatSpec with Matchers with EitherValues {
 
   it should "serialize from case class Person using implicit jsoniterBodySerializer" in {
     val person = Person("John")
-    val result = basicRequest.get(Uri("http://example.org")).body(person).body.show
+    val request = basicRequest.get(Uri("http://example.org")).body(person)
 
-    val expectedResult = "string: {\"name\":\"John\"}"
+    val expectedBody = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedContentType = Some("application/json; charset=utf-8")
 
-    result should be(expectedResult)
+    request.contentType should be(expectedContentType)
+    request.body.show should be(expectedBody)
   }
 
   def extractBody[T](request: PartialRequest[T]): String =
diff --git a/json/play-json/src/test/scala/sttp/client4/PlayJsonTests.scala b/json/play-json/src/test/scala/sttp/client4/PlayJsonTests.scala
index 9a3915b1db..53d1476133 100644
--- a/json/play-json/src/test/scala/sttp/client4/PlayJsonTests.scala
+++ b/json/play-json/src/test/scala/sttp/client4/PlayJsonTests.scala
@@ -104,11 +104,13 @@ class PlayJsonTests extends AnyFlatSpec with Matchers with EitherValues {
     val fields: Seq[(String, JsValue)] =
       Seq[(String, JsValue)](("location", JsString("hometown")), ("bio", JsString("Scala programmer")))
     val json: JsObject = JsObject(fields)
-    val result = basicRequest.get(Uri("http://example.org")).body(json).body.show
+    val request = basicRequest.get(Uri("http://example.org")).body(json)
 
-    val expectedResult = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedBody = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedContentType = Some("application/json; charset=utf-8")
 
-    result should be(expectedResult)
+    request.contentType should be(expectedContentType)
+    request.body.show should be(expectedBody)
   }
 
   case class Inner(a: Int, b: Boolean, c: String)
diff --git a/json/spray-json/src/test/scala/sttp/client4/SprayJsonTests.scala b/json/spray-json/src/test/scala/sttp/client4/SprayJsonTests.scala
index af7ccf61a4..10caaee497 100644
--- a/json/spray-json/src/test/scala/sttp/client4/SprayJsonTests.scala
+++ b/json/spray-json/src/test/scala/sttp/client4/SprayJsonTests.scala
@@ -82,11 +82,13 @@ class SprayJsonTests extends AnyFlatSpec with Matchers with EitherValues {
       "location" -> "hometown".toJson,
       "bio" -> "Scala programmer".toJson
     )
-    val result = basicRequest.get(Uri("http://example.org")).body(json).body.show
+    val request = basicRequest.get(Uri("http://example.org")).body(json)
 
-    val expectedResult = "string: {\"bio\":\"Scala programmer\",\"location\":\"hometown\"}"
+    val expectedBody = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedContentType = Some("application/json; charset=utf-8")
 
-    result should be(expectedResult)
+    request.contentType should be(expectedContentType)
+    request.body.show should be(expectedBody)
   }
 
   def extractBody[T](request: PartialRequest[T]): String =
diff --git a/json/upickle/src/test/scala/sttp/client4/upicklejson/UpickleTests.scala b/json/upickle/src/test/scala/sttp/client4/upicklejson/UpickleTests.scala
index e96a12ed9f..3b55e94816 100644
--- a/json/upickle/src/test/scala/sttp/client4/upicklejson/UpickleTests.scala
+++ b/json/upickle/src/test/scala/sttp/client4/upicklejson/UpickleTests.scala
@@ -93,11 +93,13 @@ class UpickleTests extends AnyFlatSpec with Matchers with EitherValues {
       "location" -> "hometown",
       "bio" -> "Scala programmer"
     )
-    val result = basicRequest.get(Uri("http://example.org")).body(json).body.show
+    val request = basicRequest.get(Uri("http://example.org")).body(json)
 
-    val expectedResult = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedBody = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedContentType = Some("application/json; charset=utf-8")
 
-    result should be(expectedResult)
+    request.contentType should be(expectedContentType)
+    request.body.show should be(expectedBody)
   }
 
   case class Inner(a: Int, b: Boolean, c: String)
diff --git a/json/zio-json/src/test/scala/sttp/client4/ziojson/ZioJsonTests.scala b/json/zio-json/src/test/scala/sttp/client4/ziojson/ZioJsonTests.scala
index 2238834191..18d10bc0e7 100644
--- a/json/zio-json/src/test/scala/sttp/client4/ziojson/ZioJsonTests.scala
+++ b/json/zio-json/src/test/scala/sttp/client4/ziojson/ZioJsonTests.scala
@@ -94,11 +94,13 @@ class ZioJsonTests extends AnyFlatSpec with Matchers with EitherValues {
   it should "serialize from Json.Obj using implicit zioJsonBodySerializer" in {
     val fields: Chunk[(String, Json)] = Chunk(("location", Json.Str("hometown")), ("bio", Json.Str("Scala programmer")))
     val jObject: Json.Obj = Json.Obj(fields)
-    val result = basicRequest.get(Uri("http://example.org")).body(jObject).body.show
+    val request = basicRequest.get(Uri("http://example.org")).body(jObject)
 
-    val expectedResult = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedBody = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedContentType = Some("application/json; charset=utf-8")
 
-    result should be(expectedResult)
+    request.contentType should be(expectedContentType)
+    request.body.show should be(expectedBody)
   }
 
   def extractBody[T](request: PartialRequest[T]): String =
diff --git a/json/zio1-json/src/test/scala/sttp/client4/ziojson/ZioJsonTests.scala b/json/zio1-json/src/test/scala/sttp/client4/ziojson/ZioJsonTests.scala
index 2238834191..18d10bc0e7 100644
--- a/json/zio1-json/src/test/scala/sttp/client4/ziojson/ZioJsonTests.scala
+++ b/json/zio1-json/src/test/scala/sttp/client4/ziojson/ZioJsonTests.scala
@@ -94,11 +94,13 @@ class ZioJsonTests extends AnyFlatSpec with Matchers with EitherValues {
   it should "serialize from Json.Obj using implicit zioJsonBodySerializer" in {
     val fields: Chunk[(String, Json)] = Chunk(("location", Json.Str("hometown")), ("bio", Json.Str("Scala programmer")))
     val jObject: Json.Obj = Json.Obj(fields)
-    val result = basicRequest.get(Uri("http://example.org")).body(jObject).body.show
+    val request = basicRequest.get(Uri("http://example.org")).body(jObject)
 
-    val expectedResult = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedBody = "string: {\"location\":\"hometown\",\"bio\":\"Scala programmer\"}"
+    val expectedContentType = Some("application/json; charset=utf-8")
 
-    result should be(expectedResult)
+    request.contentType should be(expectedContentType)
+    request.body.show should be(expectedBody)
   }
 
   def extractBody[T](request: PartialRequest[T]): String =