d.correlate: exit on insufficient input and fix text line counter

scripts/d.correlate/d.correlate.py

@@ -37,7 +37,7 @@ def main():
     layers = options["map"].split(",")
 
     if len(layers) < 2:
-        gcore.error(_("At least 2 maps are required"))
+        gcore.fatal(_("At least 2 maps are required"))
 
     tmpfile = gcore.tempfile()
 
@@ -55,7 +55,7 @@ def main():
     os.environ["GRASS_RENDER_FILE_READ"] = "TRUE"
 
     colors = ["red", "black", "blue", "green", "gray", "violet"]
-    line = 2
+    text_line = 2
     iloop = 0
     jloop = 0
     for iloop, i in enumerate(layers):
@@ -65,9 +65,13 @@ def main():
                 colors = colors[1:]
                 colors.append(color)
                 gcore.write_command(
-                    "d.text", color=color, size=4, line=line, stdin="%s %s" % (i, j)
+                    "d.text",
+                    color=color,
+                    size=4,
+                    line=text_line,
+                    stdin="%s %s" % (i, j),
                 )
-                line += 1
+                text_line += 1
 
                 ofile = open(tmpfile, "w")
                 gcore.run_command("r.stats", flags="cnA", input=(i, j), stdout=ofile)

scripts/d.correlate/tests/d_correlate_test.py

@@ -0,0 +1,47 @@
+"""Tests of d.correlate"""
+
+import pytest
+
+from grass.exceptions import CalledModuleError
+from grass.tools import Tools
+
+
+def render_tools(session, tmp_path):
+    """Return a Tools object for the session's mapset with an offscreen renderer.
+
+    A copy of the session environment is used, rather than mutating it, so the
+    cairo render settings do not leak into the shared session fixture.
+    d.correlate is a display tool, so the tests need a working render target;
+    without one the tool would fail at its first d.text call and mask the
+    behavior under test.
+    """
+    env = dict(session.env)
+    env["GRASS_RENDER_IMMEDIATE"] = "cairo"
+    env["GRASS_RENDER_FILE"] = str(tmp_path / "correlate.png")
+    return Tools(env=env)
+
+
+def test_fewer_than_two_maps_is_fatal(xy_raster_dataset_session_mapset, tmp_path):
+    """d.correlate must fail, not silently succeed, with fewer than two maps.
+
+    Regression test: a single map previously printed an error but still exited
+    with a success code and produced no output.
+    """
+    tools = render_tools(xy_raster_dataset_session_mapset, tmp_path)
+    tools.r_mapcalc(expression="map_a = 1")
+    with pytest.raises(CalledModuleError):
+        tools.d_correlate(map="map_a")
+
+
+def test_more_than_two_maps_runs(xy_raster_dataset_session_mapset, tmp_path):
+    """d.correlate handles more than two maps without crashing.
+
+    Regression test: the per-pair text line counter was reused as the
+    file-iteration variable, raising a TypeError on the second map pair (that
+    is, whenever three or more maps were given).
+    """
+    tools = render_tools(xy_raster_dataset_session_mapset, tmp_path)
+    tools.r_mapcalc(expression="map_a = 1")
+    tools.r_mapcalc(expression="map_b = col()")
+    tools.r_mapcalc(expression="map_c = row()")
+    tools.d_correlate(map="map_a,map_b,map_c")