Fixed getting value test for tensors

kmath-core/src/commonMain/kotlin/space/kscience/kmath/tensors/RealTensorAlgebra.kt

@@ -3,8 +3,6 @@ package space.kscience.kmath.tensors
 import space.kscience.kmath.nd.MutableNDBuffer
 import space.kscience.kmath.structures.RealBuffer
 import space.kscience.kmath.structures.array
-import kotlin.js.JsName
-import kotlin.math.abs
 
 
 public class RealTensor(
@@ -19,11 +17,9 @@ public class RealTensor(
 
 public class RealTensorAlgebra : TensorPartialDivisionAlgebra<Double, RealTensor> {
 
-    //rename to item?
     override fun RealTensor.value(): Double {
-        check(this.dimension == 0) {
-            // todo change message
-            "This tensor has shape ${shape.toList()}"
+        check(this.shape contentEquals  intArrayOf(1)) {
+            "Inconsistent value for tensor of shape ${shape.toList()}"
         }
         return this.buffer.array[0]
     }

kmath-core/src/commonMain/kotlin/space/kscience/kmath/tensors/TensorStrides.kt

@@ -48,5 +48,5 @@ public class TensorStrides(override val shape: IntArray): Strides
         indexFromOffset(offset, strides, shape.size)
 
     override val linearSize: Int
-        get() = shape.fold(1) { acc, i -> acc * i }
+        get() = shape.reduce(Int::times)
 }

kmath-core/src/commonTest/kotlin/space/kscience/kmath/tensors/TestRealTensor.kt

@@ -9,9 +9,9 @@ import kotlin.test.assertTrue
 class TestRealTensor {
 
     @Test
-    fun valueTest(){
+    fun valueTest() = RealTensorAlgebra {
         val value = 12.5
-        val tensor = RealTensor(IntArray(0), doubleArrayOf(value))
+        val tensor = RealTensor(intArrayOf(1), doubleArrayOf(value))
         assertEquals(tensor.value(), value)
     }