diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/ErrorsForCasesWithoutExamplesTestCase.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/ErrorsForCasesWithoutExamplesTestCase.java
index 0230aded525be..051655ae96f50 100644
--- a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/ErrorsForCasesWithoutExamplesTestCase.java
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/ErrorsForCasesWithoutExamplesTestCase.java
@@ -22,6 +22,7 @@
 import java.util.stream.Stream;
 
 import static org.elasticsearch.xpack.esql.EsqlTestUtils.randomLiteral;
+import static org.hamcrest.Matchers.greaterThan;
 
 public abstract class ErrorsForCasesWithoutExamplesTestCase extends ESTestCase {
     protected abstract List<TestCaseSupplier> cases();
@@ -68,6 +69,7 @@ public final void test() {
             checked++;
         }
         logger.info("checked {} signatures", checked);
+        assertThat(checked, greaterThan(0));
     }
 
     private Stream<List<DataType>> missingSignatures(List<TestCaseSupplier> cases, Set<List<DataType>> valid) {
diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LeftErrorTests.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LeftErrorTests.java
new file mode 100644
index 0000000000000..44b9c13e1baa6
--- /dev/null
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LeftErrorTests.java
@@ -0,0 +1,41 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+package org.elasticsearch.xpack.esql.expression.function.scalar.string;
+
+import org.elasticsearch.xpack.esql.core.expression.Expression;
+import org.elasticsearch.xpack.esql.core.tree.Source;
+import org.elasticsearch.xpack.esql.core.type.DataType;
+import org.elasticsearch.xpack.esql.expression.function.ErrorsForCasesWithoutExamplesTestCase;
+import org.elasticsearch.xpack.esql.expression.function.TestCaseSupplier;
+import org.hamcrest.Matcher;
+
+import java.util.List;
+import java.util.Set;
+
+import static org.hamcrest.Matchers.equalTo;
+
+public class LeftErrorTests extends ErrorsForCasesWithoutExamplesTestCase {
+    @Override
+    protected List<TestCaseSupplier> cases() {
+        return paramsToSuppliers(LeftTests.parameters());
+    }
+
+    @Override
+    protected Expression build(Source source, List<Expression> args) {
+        return new Left(source, args.get(0), args.get(1));
+    }
+
+    @Override
+    protected Matcher<String> expectedTypeErrorMatcher(List<Set<DataType>> validPerPosition, List<DataType> signature) {
+        return equalTo(typeErrorMessage(true, validPerPosition, signature, (v, p) -> switch (p) {
+            case 0 -> "string";
+            case 1 -> "integer";
+            default -> "";
+        }));
+    }
+}
diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LeftTests.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LeftTests.java
index e4e54a9e0935f..2a194a39d34e5 100644
--- a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LeftTests.java
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LeftTests.java
@@ -181,11 +181,7 @@ public static Iterable<Object[]> parameters() {
             );
         }));
 
-        return parameterSuppliersFromTypedDataWithDefaultChecks(true, suppliers, (v, p) -> switch (p) {
-            case 0 -> "string";
-            case 1 -> "integer";
-            default -> "";
-        });
+        return parameterSuppliersFromTypedDataWithDefaultChecksNoErrors(true, suppliers);
     }
 
     private static String unicodeLeftSubstring(String str, int length) {
diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LengthErrorTests.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LengthErrorTests.java
new file mode 100644
index 0000000000000..ca8f2cb208209
--- /dev/null
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LengthErrorTests.java
@@ -0,0 +1,37 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+package org.elasticsearch.xpack.esql.expression.function.scalar.string;
+
+import org.elasticsearch.xpack.esql.core.expression.Expression;
+import org.elasticsearch.xpack.esql.core.tree.Source;
+import org.elasticsearch.xpack.esql.core.type.DataType;
+import org.elasticsearch.xpack.esql.expression.function.ErrorsForCasesWithoutExamplesTestCase;
+import org.elasticsearch.xpack.esql.expression.function.TestCaseSupplier;
+import org.hamcrest.Matcher;
+
+import java.util.List;
+import java.util.Set;
+
+import static org.hamcrest.Matchers.equalTo;
+
+public class LengthErrorTests extends ErrorsForCasesWithoutExamplesTestCase {
+    @Override
+    protected List<TestCaseSupplier> cases() {
+        return paramsToSuppliers(LengthTests.parameters());
+    }
+
+    @Override
+    protected Expression build(Source source, List<Expression> args) {
+        return new Length(source, args.get(0));
+    }
+
+    @Override
+    protected Matcher<String> expectedTypeErrorMatcher(List<Set<DataType>> validPerPosition, List<DataType> signature) {
+        return equalTo(typeErrorMessage(false, validPerPosition, signature, (v, p) -> "string"));
+    }
+}
diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LengthTests.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LengthTests.java
index ba4c8c8ce1ea4..3ef24ff4eba70 100644
--- a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LengthTests.java
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/LengthTests.java
@@ -49,7 +49,7 @@ public static Iterable<Object[]> parameters() {
         cases.addAll(makeTestCases("6 bytes, 2 code points", () -> "❗️", 2));
         cases.addAll(makeTestCases("100 random alpha", () -> randomAlphaOfLength(100), 100));
         cases.addAll(makeTestCases("100 random code points", () -> randomUnicodeOfCodepointLength(100), 100));
-        return parameterSuppliersFromTypedDataWithDefaultChecks(true, cases, (v, p) -> "string");
+        return parameterSuppliersFromTypedDataWithDefaultChecksNoErrors(true, cases);
     }
 
     private static List<TestCaseSupplier> makeTestCases(String title, Supplier<String> text, int expectedLength) {
@@ -87,10 +87,6 @@ private static List<TestCaseSupplier> makeTestCases(String title, Supplier<Strin
         );
     }
 
-    private Matcher<Object> resultsMatcher(List<TestCaseSupplier.TypedData> typedData) {
-        return equalTo(UnicodeUtil.codePointCount((BytesRef) typedData.get(0).data()));
-    }
-
     @Override
     protected Expression build(Source source, List<Expression> args) {
         return new Length(source, args.get(0));
diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/RightErrorTests.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/RightErrorTests.java
new file mode 100644
index 0000000000000..3b90a26fb908f
--- /dev/null
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/RightErrorTests.java
@@ -0,0 +1,41 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+package org.elasticsearch.xpack.esql.expression.function.scalar.string;
+
+import org.elasticsearch.xpack.esql.core.expression.Expression;
+import org.elasticsearch.xpack.esql.core.tree.Source;
+import org.elasticsearch.xpack.esql.core.type.DataType;
+import org.elasticsearch.xpack.esql.expression.function.ErrorsForCasesWithoutExamplesTestCase;
+import org.elasticsearch.xpack.esql.expression.function.TestCaseSupplier;
+import org.hamcrest.Matcher;
+
+import java.util.List;
+import java.util.Set;
+
+import static org.hamcrest.Matchers.equalTo;
+
+public class RightErrorTests extends ErrorsForCasesWithoutExamplesTestCase {
+    @Override
+    protected List<TestCaseSupplier> cases() {
+        return paramsToSuppliers(RightTests.parameters());
+    }
+
+    @Override
+    protected Expression build(Source source, List<Expression> args) {
+        return new Right(source, args.get(0), args.get(1));
+    }
+
+    @Override
+    protected Matcher<String> expectedTypeErrorMatcher(List<Set<DataType>> validPerPosition, List<DataType> signature) {
+        return equalTo(typeErrorMessage(true, validPerPosition, signature, (v, p) -> switch (p) {
+            case 0 -> "string";
+            case 1 -> "integer";
+            default -> "";
+        }));
+    }
+}
diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/RightTests.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/RightTests.java
index bf93ef42ed6ad..1a65407e538c2 100644
--- a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/RightTests.java
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/RightTests.java
@@ -179,11 +179,7 @@ public static Iterable<Object[]> parameters() {
                 equalTo(new BytesRef(unicodeRightSubstring(text, length)))
             );
         }));
-        return parameterSuppliersFromTypedDataWithDefaultChecks(true, suppliers, (v, p) -> switch (p) {
-            case 0 -> "string";
-            case 1 -> "integer";
-            default -> throw new IllegalStateException("bad parameter number");
-        });
+        return parameterSuppliersFromTypedDataWithDefaultChecksNoErrors(true, suppliers);
     }
 
     private static String unicodeRightSubstring(String str, int length) {
diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/SpaceErrorTests.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/SpaceErrorTests.java
new file mode 100644
index 0000000000000..ff53bf1079c3d
--- /dev/null
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/SpaceErrorTests.java
@@ -0,0 +1,37 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+package org.elasticsearch.xpack.esql.expression.function.scalar.string;
+
+import org.elasticsearch.xpack.esql.core.expression.Expression;
+import org.elasticsearch.xpack.esql.core.tree.Source;
+import org.elasticsearch.xpack.esql.core.type.DataType;
+import org.elasticsearch.xpack.esql.expression.function.ErrorsForCasesWithoutExamplesTestCase;
+import org.elasticsearch.xpack.esql.expression.function.TestCaseSupplier;
+import org.hamcrest.Matcher;
+
+import java.util.List;
+import java.util.Set;
+
+import static org.hamcrest.Matchers.equalTo;
+
+public class SpaceErrorTests extends ErrorsForCasesWithoutExamplesTestCase {
+    @Override
+    protected List<TestCaseSupplier> cases() {
+        return paramsToSuppliers(SpaceTests.parameters());
+    }
+
+    @Override
+    protected Expression build(Source source, List<Expression> args) {
+        return new Space(source, args.get(0));
+    }
+
+    @Override
+    protected Matcher<String> expectedTypeErrorMatcher(List<Set<DataType>> validPerPosition, List<DataType> signature) {
+        return equalTo(typeErrorMessage(false, validPerPosition, signature,(v, p) -> "integer"));
+    }
+}
diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/SpaceTests.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/SpaceTests.java
index 308ce2c9d932f..40c9b33609a31 100644
--- a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/SpaceTests.java
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/SpaceTests.java
@@ -71,7 +71,7 @@ public static Iterable<Object[]> parameters() {
                 .withFoldingException(IllegalArgumentException.class, "Creating strings longer than [" + max + "] bytes is not supported");
         }));
 
-        return parameterSuppliersFromTypedDataWithDefaultChecks(true, cases, (v, p) -> "integer");
+        return parameterSuppliersFromTypedDataWithDefaultChecksNoErrors(true, cases);
     }
 
     @Override
diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToLowerErrorTests.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToLowerErrorTests.java
new file mode 100644
index 0000000000000..2ce40f561efe6
--- /dev/null
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToLowerErrorTests.java
@@ -0,0 +1,38 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+package org.elasticsearch.xpack.esql.expression.function.scalar.string;
+
+import org.elasticsearch.xpack.esql.EsqlTestUtils;
+import org.elasticsearch.xpack.esql.core.expression.Expression;
+import org.elasticsearch.xpack.esql.core.tree.Source;
+import org.elasticsearch.xpack.esql.core.type.DataType;
+import org.elasticsearch.xpack.esql.expression.function.ErrorsForCasesWithoutExamplesTestCase;
+import org.elasticsearch.xpack.esql.expression.function.TestCaseSupplier;
+import org.hamcrest.Matcher;
+
+import java.util.List;
+import java.util.Set;
+
+import static org.hamcrest.Matchers.equalTo;
+
+public class ToLowerErrorTests extends ErrorsForCasesWithoutExamplesTestCase {
+    @Override
+    protected List<TestCaseSupplier> cases() {
+        return paramsToSuppliers(ToLowerTests.parameters());
+    }
+
+    @Override
+    protected Expression build(Source source, List<Expression> args) {
+        return new ToLower(source, args.get(0), EsqlTestUtils.TEST_CFG);
+    }
+
+    @Override
+    protected Matcher<String> expectedTypeErrorMatcher(List<Set<DataType>> validPerPosition, List<DataType> signature) {
+        return equalTo(typeErrorMessage(false, validPerPosition, signature,(v, p) -> "string"));
+    }
+}
diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToLowerTests.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToLowerTests.java
index 026d190c06e3f..b355feb6130a3 100644
--- a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToLowerTests.java
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToLowerTests.java
@@ -47,9 +47,7 @@ public static Iterable<Object[]> parameters() {
         suppliers.add(supplier("text unicode", DataType.TEXT, () -> randomUnicodeOfLengthBetween(1, 10)));
         suppliers.add(supplier("semantic_text ascii", DataType.SEMANTIC_TEXT, () -> randomAlphaOfLengthBetween(1, 10)));
         suppliers.add(supplier("semantic_text unicode", DataType.SEMANTIC_TEXT, () -> randomUnicodeOfLengthBetween(1, 10)));
-
-        // add null as parameter
-        return parameterSuppliersFromTypedDataWithDefaultChecks(true, suppliers, (v, p) -> "string");
+        return parameterSuppliersFromTypedDataWithDefaultChecksNoErrors(true, suppliers);
     }
 
     public void testRandomLocale() {
diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToUpperErrorTests.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToUpperErrorTests.java
new file mode 100644
index 0000000000000..025f206ebbb2d
--- /dev/null
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToUpperErrorTests.java
@@ -0,0 +1,38 @@
+/*
+ * Copyright Elasticsearch B.V. and/or licensed to Elasticsearch B.V. under one
+ * or more contributor license agreements. Licensed under the Elastic License
+ * 2.0; you may not use this file except in compliance with the Elastic License
+ * 2.0.
+ */
+
+package org.elasticsearch.xpack.esql.expression.function.scalar.string;
+
+import org.elasticsearch.xpack.esql.EsqlTestUtils;
+import org.elasticsearch.xpack.esql.core.expression.Expression;
+import org.elasticsearch.xpack.esql.core.tree.Source;
+import org.elasticsearch.xpack.esql.core.type.DataType;
+import org.elasticsearch.xpack.esql.expression.function.ErrorsForCasesWithoutExamplesTestCase;
+import org.elasticsearch.xpack.esql.expression.function.TestCaseSupplier;
+import org.hamcrest.Matcher;
+
+import java.util.List;
+import java.util.Set;
+
+import static org.hamcrest.Matchers.equalTo;
+
+public class ToUpperErrorTests extends ErrorsForCasesWithoutExamplesTestCase {
+    @Override
+    protected List<TestCaseSupplier> cases() {
+        return paramsToSuppliers(ToUpperTests.parameters());
+    }
+
+    @Override
+    protected Expression build(Source source, List<Expression> args) {
+        return new ToUpper(source, args.get(0), EsqlTestUtils.TEST_CFG);
+    }
+
+    @Override
+    protected Matcher<String> expectedTypeErrorMatcher(List<Set<DataType>> validPerPosition, List<DataType> signature) {
+        return equalTo(typeErrorMessage(false, validPerPosition, signature,(v, p) -> "string"));
+    }
+}
diff --git a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToUpperTests.java b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToUpperTests.java
index 027ac54d15875..fdae4f953a0fa 100644
--- a/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToUpperTests.java
+++ b/x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/expression/function/scalar/string/ToUpperTests.java
@@ -47,9 +47,7 @@ public static Iterable<Object[]> parameters() {
         suppliers.add(supplier("text unicode", DataType.TEXT, () -> randomUnicodeOfLengthBetween(1, 10)));
         suppliers.add(supplier("semantic_text ascii", DataType.SEMANTIC_TEXT, () -> randomAlphaOfLengthBetween(1, 10)));
         suppliers.add(supplier("semantic_text unicode", DataType.SEMANTIC_TEXT, () -> randomUnicodeOfLengthBetween(1, 10)));
-
-        // add null as parameter
-        return parameterSuppliersFromTypedDataWithDefaultChecks(true, suppliers, (v, p) -> "string");
+        return parameterSuppliersFromTypedDataWithDefaultChecksNoErrors(true, suppliers);
     }
 
     public void testRandomLocale() {