Test for constraint in message

tests/functional/test_new_resolver_errors.py

@@ -24,3 +24,24 @@ def test_new_resolver_conflict_requirements_file(tmpdir, script):
 
     message = "package versions have conflicting dependencies"
     assert message in result.stderr, str(result)
+
+
+def test_new_resolver_conflict_constraints_file(tmpdir, script):
+    create_basic_wheel_for_package(script, "pkg", "1.0")
+
+    constrats_file = tmpdir.joinpath("constraints.txt")
+    constrats_file.write_text("pkg!=1.0")
+
+    result = script.pip(
+        "install",
+        "--no-cache-dir", "--no-index",
+        "--find-links", script.scratch_path,
+        "-c", constrats_file,
+        "pkg==1.0",
+        expect_error=True,
+    )
+
+    assert "ResolutionImpossible" in result.stderr, str(result)
+
+    message = "The user requested (constraint) pkg!=1.0",
+    assert message in result.stdout, str(result)