test: add negative test for reserved keyword in module import diagnostic

Adds a test case verifying that when a reserved keyword (e.g. 'client')
is used unescaped in a module import path, the diagnostic message
correctly includes the keyword in the module path string.

Regression test for #44509 and #44519.

Author: notdulain

tests/jballerina-unit-test/src/test/java/org/ballerinalang/test/imports/ImportsNegativeTests.java

@@ -56,4 +56,16 @@ public void testInvalidAutoImports() {
         validateError(result, index++, "unknown type 'CallStackElement'", 51, 30);
         assertEquals(result.getErrorCount(), index);
     }
+
+    @Test(description = "Test diagnostic message for reserved keyword in module import path")
+    public void testReservedKeywordInModuleImportDiagnostic() {
+        CompileResult result = BCompileUtil.compile("test-src/imports/ReservedKeywordImportTestProject");
+        int index = 0;
+        // 'client' is a reserved keyword; the diagnostic must include it in the module path,
+        // i.e. "ballerinax/client.config", not "ballerinax/.config" (regression for #44509/#44519)
+        validateError(result, index++, "invalid token 'client'", 5, 19);
+        validateError(result, index++, "missing identifier", 5, 19);
+        validateError(result, index++, "cannot resolve module 'ballerinax/client.config as config'", 5, 1);
+        assertEquals(result.getErrorCount(), index);
+    }
 }

tests/jballerina-unit-test/src/test/resources/test-src/imports/ReservedKeywordImportTestProject/Ballerina.toml

@@ -0,0 +1,4 @@
+[package]
+org = "testorg"
+name = "reservedkeywordimport"
+version = "1.0.0"

tests/jballerina-unit-test/src/test/resources/test-src/imports/ReservedKeywordImportTestProject/reserved-keyword-import-negative.bal

@@ -0,0 +1,5 @@
+// Test: using a reserved keyword (client) in a module import path without '^' escape
+// should produce a diagnostic that includes the keyword in the module path,
+// i.e. "cannot resolve module 'ballerinax/client.config as config'"
+// NOT "cannot resolve module 'ballerinax/.config as config'"
+import ballerinax/client.config;