[C API] NP_GetType implementation (#419)

### Summary:
Continue with basic implementation of a C API for Neuropod. Issue #407

### Test Plan:
Added test for input and output tensors.

source/neuropod/bindings/c/c_api.cc

@@ -21,6 +21,7 @@ limitations under the License.
 #include "neuropod/bindings/c/np_status_internal.h"
 #include "neuropod/bindings/c/np_tensor_allocator_internal.h"
 #include "neuropod/bindings/c/np_valuemap_internal.h"
+#include "neuropod/core/generic_tensor.hh"
 
 #include <exception>
 #include <string>
@@ -137,3 +138,10 @@ NP_TensorAllocator *NP_GetAllocator(NP_Neuropod *model)
     out->allocator = model->model->get_tensor_allocator();
     return out;
 }
+
+NP_TensorAllocator *NP_GetGenericAllocator()
+{
+    auto out       = new NP_TensorAllocator();
+    out->allocator = neuropod::get_generic_tensor_allocator();
+    return out;
+}

source/neuropod/bindings/c/c_api.h

@@ -122,6 +122,10 @@ NP_TensorSpec *NP_GetOutputSpec(NP_Neuropod *model, size_t index);
 // Note: The caller is responsible for freeing the returned TensorAllocator
 NP_TensorAllocator *NP_GetAllocator(NP_Neuropod *model);
 
+// Get a generic allocator to allocate generic tensors that is usefull for tests.
+// Note: The caller is responsible for freeing the returned TensorAllocator
+NP_TensorAllocator *NP_GetGenericAllocator();
+
 #ifdef __cplusplus
 }
 #endif

source/neuropod/bindings/c/np_tensor.cc

@@ -18,6 +18,11 @@ limitations under the License.
 #include "neuropod/bindings/c/np_tensor_internal.h"
 #include "neuropod/internal/neuropod_tensor_raw_data_access.hh"
 
+NP_TensorType NP_GetType(const NP_NeuropodTensor *tensor)
+{
+    return static_cast<NP_TensorType>(tensor->tensor->as_tensor()->get_tensor_type());
+}
+
 void *NP_GetData(NP_NeuropodTensor *tensor)
 {
     return neuropod::internal::NeuropodTensorRawDataAccess::get_untyped_data_ptr(*tensor->tensor->as_tensor());

source/neuropod/tests/test_c_api.c

@@ -105,6 +105,9 @@ static void TestLoadAndInference(void)
     NP_InsertTensor(inputs, "x", x);
     NP_InsertTensor(inputs, "y", y);
 
+    ASSERT_EQ(NP_GetType(x), FLOAT_TENSOR);
+    ASSERT_EQ(NP_GetType(y), FLOAT_TENSOR);
+
     // Free the input tensors
     NP_FreeTensor(x);
     NP_FreeTensor(y);
@@ -124,6 +127,9 @@ static void TestLoadAndInference(void)
     NP_NeuropodTensor *out       = NP_GetTensor(outputs, "out");
     float *            out_data  = (float *) NP_GetData(out);
     size_t             nout_data = NP_GetNumElements(out);
+
+    ASSERT_EQ(NP_GetType(out), FLOAT_TENSOR);
+
     for (size_t i = 0; i < nout_data; ++i)
     {
         ASSERT_EQ(out_data[i], target[i]);
@@ -231,10 +237,33 @@ static void TestLoadAndInferenceWithOptions(void)
     NP_FreeNeuropod(model);
 }
 
+static void TestTensorGetters(void)
+{
+    NP_TensorAllocator *allocator = NP_GetGenericAllocator();
+    ASSERT_NE(allocator, NULL);
+
+    // Create tensors with different types and test it.
+    int64_t            dims[] = {2, 2};
+    NP_NeuropodTensor *x      = NP_AllocateTensor(allocator, sizeof(dims) / sizeof(int64_t), dims, FLOAT_TENSOR);
+    NP_NeuropodTensor *y      = NP_AllocateTensor(allocator, sizeof(dims) / sizeof(int64_t), dims, DOUBLE_TENSOR);
+    NP_NeuropodTensor *z      = NP_AllocateTensor(allocator, sizeof(dims) / sizeof(int64_t), dims, STRING_TENSOR);
+
+    ASSERT_EQ(NP_GetType(x), FLOAT_TENSOR);
+    ASSERT_EQ(NP_GetType(y), DOUBLE_TENSOR);
+    ASSERT_EQ(NP_GetType(z), STRING_TENSOR);
+
+    NP_FreeTensor(x);
+    NP_FreeTensor(y);
+    NP_FreeTensor(z);
+
+    NP_FreeAllocator(allocator);
+}
+
 static void RunTests(void)
 {
     TestLoadAndInference();
     TestLoadAndInferenceWithOptions();
+    TestTensorGetters();
 }
 
 int main(void)