test: ipa: Add failing test for single point Pwl

Sometimes it is useful to have a Pwl with only a single point defined.
A practical use case is tuning files with only a single entry for Pwl
related parameters, where the expectation is that this entry just gets
used.

Add a failing test case for such a single point Pwl.

Signed-off-by: Stefan Klug <stefan.klug@ideasonboard.com>
Reviewed-by: Kieran Bingham <kieran.bingham@ideasonboard.com>

test/ipa/libipa/meson.build

@@ -4,7 +4,7 @@ libipa_test = [
     {'name': 'fixedpoint', 'sources': ['fixedpoint.cpp']},
     {'name': 'histogram', 'sources': ['histogram.cpp']},
     {'name': 'interpolator', 'sources': ['interpolator.cpp']},
-    {'name': 'pwl', 'sources': ['pwl.cpp']},
+    {'name': 'pwl', 'sources': ['pwl.cpp'], 'should_fail': true },
 ]
 
 foreach test : libipa_test

test/ipa/libipa/pwl.cpp

@@ -43,6 +43,13 @@ protected:
 
 		ASSERT_EQ(pwl.size(), 2);
 
+		/* Test degenerate PWL. */
+		pwl.clear();
+		pwl.append(1, 1);
+		ASSERT_EQ(pwl.eval(0), 1);
+		ASSERT_EQ(pwl.eval(1), 1);
+		ASSERT_EQ(pwl.eval(2), 1);
+
 		return TestPass;
 	}
 };