Better assertion failures for containJsonKeyValue (#3949)

Now prints whether the key was missing, or if it had wrong value

<!-- 
If this PR updates documentation, please update all relevant versions of
the docs, see:
https://github.com/kotest/kotest/tree/master/documentation/versioned_docs
The documentation at
https://github.com/kotest/kotest/tree/master/documentation/docs is the
documentation for the next minor or major version _TO BE RELEASED_
-->

kotest-assertions/kotest-assertions-json/src/jvmMain/kotlin/io/kotest/assertions/json/keyvalues.kt

@@ -3,6 +3,10 @@ package io.kotest.assertions.json
 import com.jayway.jsonpath.InvalidPathException
 import com.jayway.jsonpath.JsonPath
 import com.jayway.jsonpath.PathNotFoundException
+import io.kotest.assertions.Actual
+import io.kotest.assertions.Expected
+import io.kotest.assertions.intellijFormatError
+import io.kotest.assertions.print.print
 import io.kotest.matchers.Matcher
 import io.kotest.matchers.MatcherResult
 import io.kotest.matchers.should
@@ -21,23 +25,42 @@ inline fun <reified T> String.shouldNotContainJsonKeyValue(path: String, value:
    this shouldNot containJsonKeyValue(path, value)
 
 inline fun <reified T> containJsonKeyValue(path: String, t: T) = object : Matcher<String?> {
-   override fun test(value: String?): MatcherResult {
-      val sub = when (value) {
-         null -> value
-         else -> if (value.length < 50) value.trim() else value.substring(0, 50).trim() + "..."
-      }
+   private fun keyIsAbsentFailure() = MatcherResult(
+      false,
+      { "Expected given to contain json key <'$path'> but key was not found." },
+      { "Expected given to not contain json key <'$path'> but key was found." }
+   )
 
-      val passed = value != null && try {
-         JsonPath.parse(value).read(path, T::class.java) == t
+   private fun invalidJsonFailure(actualJson: String?) = MatcherResult(
+      false,
+      { "Expected a valid JSON, but was ${if (actualJson == null) "null" else "empty" }" },
+      { "Expected a valid JSON, but was ${if (actualJson == null) "null" else "empty" }" },
+   )
+
+   private fun extractKey(value: String?): T? {
+      return try {
+         JsonPath.parse(value).read(path, T::class.java)
       } catch (e: PathNotFoundException) {
-         false
+         null
       } catch (e: InvalidPathException) {
          throw AssertionError("$path is not a valid JSON path")
       }
+   }
+
+   override fun test(value: String?): MatcherResult {
+      if (value.isNullOrEmpty()) return invalidJsonFailure(value)
+
+      val sub =
+         if (value.length < 50) value.trim()
+         else value.substring(0, 50).trim() + "..."
+
+      val actualKeyValue = extractKey(value)
+      val passed = t == actualKeyValue
+      if (!passed && actualKeyValue == null) return keyIsAbsentFailure()
 
       return MatcherResult(
          passed,
-         { "$sub should contain the element $path = $t" },
+         { "Value mismatch at '$path': ${intellijFormatError(Expected(t.print()), Actual(actualKeyValue.print()))}" },
          {
             "$sub should not contain the element $path = $t"
          }

kotest-assertions/kotest-assertions-json/src/jvmTest/kotlin/com/sksamuel/kotest/tests/json/ContainJsonKeyValueTest.kt

@@ -0,0 +1,89 @@
+package com.sksamuel.kotest.tests.json
+
+import io.kotest.assertions.asClue
+import io.kotest.assertions.json.shouldContainJsonKeyValue
+import io.kotest.assertions.json.shouldNotContainJsonKeyValue
+import io.kotest.assertions.shouldFail
+import io.kotest.assertions.throwables.shouldThrow
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+import org.intellij.lang.annotations.Language
+
+class ContainJsonKeyValueTest : StringSpec({
+   @Language("JSON")
+   val json = """
+      {
+          "store": {
+              "book": [
+                  {
+                    "category": "reference",
+                    "author": "Nigel Rees",
+                    "title": "Sayings of the Century",
+                    "price": 8.95
+                 },
+                 {
+                    "category": "fiction",
+                    "author": "Evelyn Waugh",
+                    "title": "Sword of Honour",
+                    "price": 12.99
+                 }
+              ],
+              "bicycle": {
+                 "color": "red",
+                 "price": 19.95,
+                 "code": 1
+              }
+         }
+      }
+   """.trimIndent()
+
+   "Negated assertions" {
+      "".shouldNotContainJsonKeyValue("$.store.bicycle.color", "red")
+      "{}".shouldNotContainJsonKeyValue("$.store.bicycle.color", "red")
+      """{ "foo": "bar" }""".shouldNotContainJsonKeyValue("foo", "baz")
+      shouldFail {
+         """{ "foo": "bar" }""".shouldNotContainJsonKeyValue("foo", "bar")
+      }.message shouldBe """{ "foo": "bar" } should not contain the element foo = bar"""
+   }
+
+   "Failure message states if key is missing, when it's missing" {
+      shouldFail {
+         json.shouldContainJsonKeyValue("$.bicycle.engine", "V2")
+      }.message shouldBe """
+         Expected given to contain json key <'$.bicycle.engine'> but key was not found.
+      """.trimIndent()
+   }
+
+   "Failure message states states value mismatch if key is present with different value" {
+      shouldFail {
+         json.shouldContainJsonKeyValue("$.store.book[0].price", 9.95)
+      }.message shouldBe """
+         Value mismatch at '$.store.book[0].price': expected:<9.95> but was:<8.95>
+      """.trimIndent()
+   }
+
+   "test json key value" {
+      json.shouldContainJsonKeyValue("$.store.bicycle.color", "red")
+      json.shouldContainJsonKeyValue("$.store.book[0].category", "reference")
+      json.shouldContainJsonKeyValue("$.store.book[0].price", 8.95)
+      json.shouldContainJsonKeyValue("$.store.book[1].author", "Evelyn Waugh")
+      json.shouldContainJsonKeyValue("$.store.book[1].author", "Evelyn Waugh")
+      json.shouldContainJsonKeyValue("$.store.bicycle.code", 1L)
+
+      json.shouldNotContainJsonKeyValue("$.store.book[1].author", "JK Rowling")
+
+      shouldThrow<AssertionError> { null.shouldContainJsonKeyValue("ab", "cd") }.message shouldBe
+         "Expected a valid JSON, but was null"
+
+      shouldThrow<AssertionError> { "".shouldContainJsonKeyValue("ab", "cd") }.message shouldBe
+         "Expected a valid JSON, but was empty"
+
+      "contract should work".asClue {
+         fun use(@Suppress("UNUSED_PARAMETER") json: String) {}
+
+         val nullableJson = """{"data": "value"}"""
+         nullableJson.shouldContainJsonKeyValue("data", "value")
+         use(nullableJson)
+      }
+   }
+})

kotest-assertions/kotest-assertions-json/src/jvmTest/kotlin/com/sksamuel/kotest/tests/json/JvmJsonAssertionsTest.kt

@@ -65,41 +65,6 @@ class JvmJsonAssertionsTest : StringSpec({
       }
    }
 
-   "test json key value" {
-      json.shouldContainJsonKeyValue("$.store.bicycle.color", "red")
-      json.shouldContainJsonKeyValue("$.store.book[0].category", "reference")
-      json.shouldContainJsonKeyValue("$.store.book[0].price", 8.95)
-      json.shouldContainJsonKeyValue("$.store.book[1].author", "Evelyn Waugh")
-      json.shouldContainJsonKeyValue("$.store.book[1].author", "Evelyn Waugh")
-      json.shouldContainJsonKeyValue("$.store.bicycle.code", 1L)
-
-      json.shouldNotContainJsonKeyValue("$.store.book[1].author", "JK Rowling")
-
-      shouldFail { json.shouldContainJsonKeyValue("$.store.bicycle.wheels", 2) }
-         .message shouldBe """{
-    "store": {
-        "book": [
-            {... should contain the element ${'$'}.store.bicycle.wheels = 2
-      """.trimIndent()
-
-      shouldThrow<AssertionError> {
-         json.shouldContainJsonKeyValue("$.store.book[1].author", "JK Rowling")
-      }.message shouldBe """{
-    "store": {
-        "book": [
-            {... should contain the element ${'$'}.store.book[1].author = JK Rowling"""
-
-      shouldThrow<AssertionError> { null.shouldContainJsonKeyValue("ab", "cd") }
-
-      "contract should work".asClue {
-         fun use(@Suppress("UNUSED_PARAMETER") json: String) {}
-
-         val nullableJson = """{"data": "value"}"""
-         nullableJson.shouldContainJsonKeyValue("data", "value")
-         use(nullableJson)
-      }
-   }
-
    "test json match by resource" {
 
       val testJson1 = """ { "name" : "sam", "location" : "chicago" } """