Create tests `n_dates_1` and `n_dates_14`

I had the directories `n_dates_1` and `n_dates_14`, but they did not
evolve with the code and there was not much traceability.

Inst_eddies/Tests/test_output.json

 {
+    "n_dates_1":
+    {
+	"command":
+	[
+	    "$src_dir/Inst_eddies/Analysis/write_date_range.py",
+	    "$PWD/Global_1993_2021/SHPC", "SHPC", "20454"
+	],
+	"description": "Only useful as input to other tests."
+    },
+    "n_dates_14":
+    {
+	"command":
+	[
+	    "$src_dir/Inst_eddies/Analysis/write_date_range.py",
+	    "$PWD/Global_1993_2021/SHPC", "SHPC", "20454", "-n", "14"
+	],
+	"description": "Only useful as input to other tests."
+    },
     "Medium_mix": {
 	"description": "Append to medium-sized SHPC, mixing output to the three shapefiles.",
 	"input": "&main_nml /\n",