Expand benchmarks for dataset insertion and creation

Taken from discussions in pydata#7224 (comment)

Thank you @Illviljan

asv_bench/benchmarks/merge.py

@@ -1,3 +1,5 @@
+import numpy as np
+
 import xarray as xr
 
 
@@ -13,6 +15,49 @@ def setup(self, existing_elements):
             d[f"var{i}"] = i
         self.dataset = xr.merge([d])
 
+        d = {"set_2_{i}": i for i in range(existing_elements)}
+        self.dataset2 = xr.merge([d])
+
     def time_variable_insertion(self, existing_elements):
         dataset = self.dataset
         dataset["new_var"] = 0
+
+    def time_merge_two_datasets(self, existing_elements):
+        xr.merge([self.dataset, self.dataset2])
+
+
+class DatasetCreation:
+    param_names = ["strategy", "count"]
+    params = [
+        ["dict_of_DataArrays", "dict_of_Variables", "dict_of_Tuples"],
+        [0, 1, 10, 100, 1000],
+    ]
+
+    def setup(self, strategy, count):
+        self.dataset_value = np.array(["0", "b"], dtype=str)
+        self.dataset_coords = dict(time=np.array([0, 1]))
+
+    def time_dataset_creation(self, strategy, count):
+        # The idea here is to time how long it takes to go from numpy
+        # and python data types, to a full dataset
+        # See discussion
+        # https://github.com/pydata/xarray/issues/7224#issuecomment-1292216344
+        if strategy == "dict_of_DataArrays":
+            data_vars = {
+                "long_variable_name_{i}": xr.DataArray(
+                    data=self.dataset_value, dims=("time")
+                )
+                for i in range(count)
+            }
+        elif strategy == "dict_of_Variables":
+            data_vars = {
+                "long_variable_name_{i}": xr.Variable("time", self.dataset_value)
+                for i in range(count)
+            }
+        elif strategy == "dict_of_Tuples":
+            data_vars = {
+                "long_variable_name_{i}": ("time", self.dataset_value)
+                for i in range(count)
+            }
+
+        xr.Dataset(data_vars=data_vars, coords=self.dataset_coords)