Ensure triangulate.delaunay_triples output_type is valid

Must be either one of numpy, pandas or file

Author: weiji14

pygmt/src/triangulate.py

@@ -4,6 +4,7 @@
 """
 import pandas as pd
 from pygmt.clib import Session
+from pygmt.exceptions import GMTInvalidInput
 from pygmt.helpers import (
     GMTTempFile,
     build_arg_string,
@@ -337,6 +338,12 @@ def delaunay_triples(  # pylint: disable=too-many-arguments,too-many-locals
             - None if ``outfile`` is a str (file output is stored in
               ``outfile``)
         """
+        # Return a pandas.DataFrame if ``outfile`` is not set
+        if output_type not in ["numpy", "pandas", "file"]:
+            raise GMTInvalidInput(
+                "Must specify 'output_type' either as 'numpy', 'pandas' or 'file'."
+            )
+
         # Return a pandas.DataFrame if ``outfile`` is not set
         with GMTTempFile(suffix=".txt") as tmpfile:
             if output_type != "file":

pygmt/tests/test_triangulate.py

@@ -107,6 +107,14 @@ def test_delaunay_triples_ndarray_output(dataframe, expected_dataframe):
     np.testing.assert_allclose(actual=output, desired=expected_dataframe.to_numpy())
 
 
+def test_delaunay_triples_invalid_format(dataframe):
+    """
+    Test that triangulate.delaunay_triples fails with incorrect format.
+    """
+    with pytest.raises(GMTInvalidInput):
+        triangulate.delaunay_triples(data=dataframe, output_type=1)
+
+
 def test_regular_grid_with_outgrid_true(dataframe, expected_grid):
     """
     Run triangulate.regular_grid with outgrid=True and see it load into an