diff --git a/libs/extensions/tabular/exec/src/lib/cell-range-selector-executor.spec.ts b/libs/extensions/tabular/exec/src/lib/cell-range-selector-executor.spec.ts
index a230f3356..c39d6a3c4 100644
--- a/libs/extensions/tabular/exec/src/lib/cell-range-selector-executor.spec.ts
+++ b/libs/extensions/tabular/exec/src/lib/cell-range-selector-executor.spec.ts
@@ -6,17 +6,15 @@ import * as path from 'path';
 
 import * as R from '@jvalue/jayvee-execution';
 import { getTestExecutionContext } from '@jvalue/jayvee-execution/test';
-import { TabularLangExtension } from '@jvalue/jayvee-extensions/tabular/lang';
 import {
   BlockDefinition,
   IOType,
   createJayveeServices,
-  useExtension,
 } from '@jvalue/jayvee-language-server';
 import {
   ParseHelperOptions,
-  TestLangExtension,
   expectNoParserAndLexerErrors,
+  loadTestExtensions,
   parseHelper,
   readJvTestAssetHelper,
 } from '@jvalue/jayvee-language-server/test';
@@ -67,12 +65,12 @@ describe('Validation of CellRangeSelectorExecutor', () => {
     );
   }
 
-  beforeAll(() => {
-    // Register extensions
-    useExtension(new TabularLangExtension());
-    useExtension(new TestLangExtension());
+  beforeAll(async () => {
     // Create language services
     const services = createJayveeServices(NodeFileSystem).Jayvee;
+    await loadTestExtensions(services, [
+      path.resolve(__dirname, '../../test/test-extension/TestBlockTypes.jv'),
+    ]);
     locator = services.workspace.AstNodeLocator;
     // Parse function for Jayvee (without validation)
     parse = parseHelper(services);
diff --git a/libs/extensions/tabular/exec/src/lib/cell-writer-executor.spec.ts b/libs/extensions/tabular/exec/src/lib/cell-writer-executor.spec.ts
index 28479475f..99ac1d493 100644
--- a/libs/extensions/tabular/exec/src/lib/cell-writer-executor.spec.ts
+++ b/libs/extensions/tabular/exec/src/lib/cell-writer-executor.spec.ts
@@ -6,17 +6,15 @@ import * as path from 'path';
 
 import * as R from '@jvalue/jayvee-execution';
 import { getTestExecutionContext } from '@jvalue/jayvee-execution/test';
-import { TabularLangExtension } from '@jvalue/jayvee-extensions/tabular/lang';
 import {
   BlockDefinition,
   IOType,
   createJayveeServices,
-  useExtension,
 } from '@jvalue/jayvee-language-server';
 import {
   ParseHelperOptions,
-  TestLangExtension,
   expectNoParserAndLexerErrors,
+  loadTestExtensions,
   parseHelper,
   readJvTestAssetHelper,
 } from '@jvalue/jayvee-language-server/test';
@@ -67,12 +65,12 @@ describe('Validation of CellWriterExecutor', () => {
     );
   }
 
-  beforeAll(() => {
-    // Register extensions
-    useExtension(new TabularLangExtension());
-    useExtension(new TestLangExtension());
+  beforeAll(async () => {
     // Create language services
     const services = createJayveeServices(NodeFileSystem).Jayvee;
+    await loadTestExtensions(services, [
+      path.resolve(__dirname, '../../test/test-extension/TestBlockTypes.jv'),
+    ]);
     locator = services.workspace.AstNodeLocator;
     // Parse function for Jayvee (without validation)
     parse = parseHelper(services);
diff --git a/libs/extensions/tabular/exec/src/lib/column-deleter-executor.spec.ts b/libs/extensions/tabular/exec/src/lib/column-deleter-executor.spec.ts
index e9e6ba32e..7150e817e 100644
--- a/libs/extensions/tabular/exec/src/lib/column-deleter-executor.spec.ts
+++ b/libs/extensions/tabular/exec/src/lib/column-deleter-executor.spec.ts
@@ -6,17 +6,15 @@ import * as path from 'path';
 
 import * as R from '@jvalue/jayvee-execution';
 import { getTestExecutionContext } from '@jvalue/jayvee-execution/test';
-import { TabularLangExtension } from '@jvalue/jayvee-extensions/tabular/lang';
 import {
   BlockDefinition,
   IOType,
   createJayveeServices,
-  useExtension,
 } from '@jvalue/jayvee-language-server';
 import {
   ParseHelperOptions,
-  TestLangExtension,
   expectNoParserAndLexerErrors,
+  loadTestExtensions,
   parseHelper,
   readJvTestAssetHelper,
 } from '@jvalue/jayvee-language-server/test';
@@ -67,12 +65,12 @@ describe('Validation of ColumnDeleterExecutor', () => {
     );
   }
 
-  beforeAll(() => {
-    // Register extensions
-    useExtension(new TabularLangExtension());
-    useExtension(new TestLangExtension());
+  beforeAll(async () => {
     // Create language services
     const services = createJayveeServices(NodeFileSystem).Jayvee;
+    await loadTestExtensions(services, [
+      path.resolve(__dirname, '../../test/test-extension/TestBlockTypes.jv'),
+    ]);
     locator = services.workspace.AstNodeLocator;
     // Parse function for Jayvee (without validation)
     parse = parseHelper(services);
diff --git a/libs/extensions/tabular/exec/src/lib/csv-interpreter-executor.spec.ts b/libs/extensions/tabular/exec/src/lib/csv-interpreter-executor.spec.ts
index 8405f395f..c4a8b938e 100644
--- a/libs/extensions/tabular/exec/src/lib/csv-interpreter-executor.spec.ts
+++ b/libs/extensions/tabular/exec/src/lib/csv-interpreter-executor.spec.ts
@@ -9,17 +9,15 @@ import {
   createTextFileFromLocalFile,
   getTestExecutionContext,
 } from '@jvalue/jayvee-execution/test';
-import { TabularLangExtension } from '@jvalue/jayvee-extensions/tabular/lang';
 import {
   BlockDefinition,
   IOType,
   createJayveeServices,
-  useExtension,
 } from '@jvalue/jayvee-language-server';
 import {
   ParseHelperOptions,
-  TestLangExtension,
   expectNoParserAndLexerErrors,
+  loadTestExtensions,
   parseHelper,
   readJvTestAssetHelper,
 } from '@jvalue/jayvee-language-server/test';
@@ -68,12 +66,12 @@ describe('Validation of CSVInterpreterExecutor', () => {
     );
   }
 
-  beforeAll(() => {
-    // Register extensions
-    useExtension(new TabularLangExtension());
-    useExtension(new TestLangExtension());
+  beforeAll(async () => {
     // Create language services
     const services = createJayveeServices(NodeFileSystem).Jayvee;
+    await loadTestExtensions(services, [
+      path.resolve(__dirname, '../../test/test-extension/TestBlockTypes.jv'),
+    ]);
     locator = services.workspace.AstNodeLocator;
     // Parse function for Jayvee (without validation)
     parse = parseHelper(services);
diff --git a/libs/extensions/tabular/exec/src/lib/row-deleter-executor.spec.ts b/libs/extensions/tabular/exec/src/lib/row-deleter-executor.spec.ts
index c91382169..03bea0917 100644
--- a/libs/extensions/tabular/exec/src/lib/row-deleter-executor.spec.ts
+++ b/libs/extensions/tabular/exec/src/lib/row-deleter-executor.spec.ts
@@ -6,17 +6,15 @@ import * as path from 'path';
 
 import * as R from '@jvalue/jayvee-execution';
 import { getTestExecutionContext } from '@jvalue/jayvee-execution/test';
-import { TabularLangExtension } from '@jvalue/jayvee-extensions/tabular/lang';
 import {
   BlockDefinition,
   IOType,
   createJayveeServices,
-  useExtension,
 } from '@jvalue/jayvee-language-server';
 import {
   ParseHelperOptions,
-  TestLangExtension,
   expectNoParserAndLexerErrors,
+  loadTestExtensions,
   parseHelper,
   readJvTestAssetHelper,
 } from '@jvalue/jayvee-language-server/test';
@@ -67,12 +65,12 @@ describe('Validation of RowDeleterExecutor', () => {
     );
   }
 
-  beforeAll(() => {
-    // Register extensions
-    useExtension(new TabularLangExtension());
-    useExtension(new TestLangExtension());
+  beforeAll(async () => {
     // Create language services
     const services = createJayveeServices(NodeFileSystem).Jayvee;
+    await loadTestExtensions(services, [
+      path.resolve(__dirname, '../../test/test-extension/TestBlockTypes.jv'),
+    ]);
     locator = services.workspace.AstNodeLocator;
     // Parse function for Jayvee (without validation)
     parse = parseHelper(services);
diff --git a/libs/extensions/tabular/exec/src/lib/sheet-picker-executor.spec.ts b/libs/extensions/tabular/exec/src/lib/sheet-picker-executor.spec.ts
index 9dfba7ea0..4af35e9f5 100644
--- a/libs/extensions/tabular/exec/src/lib/sheet-picker-executor.spec.ts
+++ b/libs/extensions/tabular/exec/src/lib/sheet-picker-executor.spec.ts
@@ -6,17 +6,15 @@ import * as path from 'path';
 
 import * as R from '@jvalue/jayvee-execution';
 import { getTestExecutionContext } from '@jvalue/jayvee-execution/test';
-import { TabularLangExtension } from '@jvalue/jayvee-extensions/tabular/lang';
 import {
   BlockDefinition,
   IOType,
   createJayveeServices,
-  useExtension,
 } from '@jvalue/jayvee-language-server';
 import {
   ParseHelperOptions,
-  TestLangExtension,
   expectNoParserAndLexerErrors,
+  loadTestExtensions,
   parseHelper,
   readJvTestAssetHelper,
 } from '@jvalue/jayvee-language-server/test';
@@ -67,12 +65,12 @@ describe('Validation of SheetPickerExecutor', () => {
     );
   }
 
-  beforeAll(() => {
-    // Register extensions
-    useExtension(new TabularLangExtension());
-    useExtension(new TestLangExtension());
+  beforeAll(async () => {
     // Create language services
     const services = createJayveeServices(NodeFileSystem).Jayvee;
+    await loadTestExtensions(services, [
+      path.resolve(__dirname, '../../test/test-extension/TestBlockTypes.jv'),
+    ]);
     locator = services.workspace.AstNodeLocator;
     // Parse function for Jayvee (without validation)
     parse = parseHelper(services);
diff --git a/libs/extensions/tabular/exec/src/lib/table-interpreter-executor.spec.ts b/libs/extensions/tabular/exec/src/lib/table-interpreter-executor.spec.ts
index 2d1c2b165..ff21a70e4 100644
--- a/libs/extensions/tabular/exec/src/lib/table-interpreter-executor.spec.ts
+++ b/libs/extensions/tabular/exec/src/lib/table-interpreter-executor.spec.ts
@@ -6,17 +6,15 @@ import * as path from 'path';
 
 import * as R from '@jvalue/jayvee-execution';
 import { getTestExecutionContext } from '@jvalue/jayvee-execution/test';
-import { TabularLangExtension } from '@jvalue/jayvee-extensions/tabular/lang';
 import {
   BlockDefinition,
   IOType,
   createJayveeServices,
-  useExtension,
 } from '@jvalue/jayvee-language-server';
 import {
   ParseHelperOptions,
-  TestLangExtension,
   expectNoParserAndLexerErrors,
+  loadTestExtensions,
   parseHelper,
   readJvTestAssetHelper,
 } from '@jvalue/jayvee-language-server/test';
@@ -67,12 +65,12 @@ describe('Validation of TableInterpreterExecutor', () => {
     );
   }
 
-  beforeAll(() => {
-    // Register extensions
-    useExtension(new TabularLangExtension());
-    useExtension(new TestLangExtension());
+  beforeAll(async () => {
     // Create language services
     const services = createJayveeServices(NodeFileSystem).Jayvee;
+    await loadTestExtensions(services, [
+      path.resolve(__dirname, '../../test/test-extension/TestBlockTypes.jv'),
+    ]);
     locator = services.workspace.AstNodeLocator;
     // Parse function for Jayvee (without validation)
     parse = parseHelper(services);
diff --git a/libs/extensions/tabular/exec/src/lib/table-transformer-executor.spec.ts b/libs/extensions/tabular/exec/src/lib/table-transformer-executor.spec.ts
index 4ea0dce63..a2763b1ff 100644
--- a/libs/extensions/tabular/exec/src/lib/table-transformer-executor.spec.ts
+++ b/libs/extensions/tabular/exec/src/lib/table-transformer-executor.spec.ts
@@ -6,18 +6,16 @@ import * as path from 'path';
 
 import * as R from '@jvalue/jayvee-execution';
 import { getTestExecutionContext } from '@jvalue/jayvee-execution/test';
-import { TabularLangExtension } from '@jvalue/jayvee-extensions/tabular/lang';
 import {
   BlockDefinition,
   IOType,
   PrimitiveValuetypes,
   createJayveeServices,
-  useExtension,
 } from '@jvalue/jayvee-language-server';
 import {
   ParseHelperOptions,
-  TestLangExtension,
   expectNoParserAndLexerErrors,
+  loadTestExtensions,
   parseHelper,
   readJvTestAssetHelper,
 } from '@jvalue/jayvee-language-server/test';
@@ -96,12 +94,12 @@ describe('Validation of TableTransformerExecutor', () => {
     );
   }
 
-  beforeAll(() => {
-    // Register extensions
-    useExtension(new TabularLangExtension());
-    useExtension(new TestLangExtension());
+  beforeAll(async () => {
     // Create language services
     const services = createJayveeServices(NodeFileSystem).Jayvee;
+    await loadTestExtensions(services, [
+      path.resolve(__dirname, '../../test/test-extension/TestBlockTypes.jv'),
+    ]);
     locator = services.workspace.AstNodeLocator;
     // Parse function for Jayvee (without validation)
     parse = parseHelper(services);
diff --git a/libs/extensions/tabular/exec/src/lib/xlsx-interpreter-executor.spec.ts b/libs/extensions/tabular/exec/src/lib/xlsx-interpreter-executor.spec.ts
index c2c230f8c..f289ea96d 100644
--- a/libs/extensions/tabular/exec/src/lib/xlsx-interpreter-executor.spec.ts
+++ b/libs/extensions/tabular/exec/src/lib/xlsx-interpreter-executor.spec.ts
@@ -9,17 +9,15 @@ import {
   createBinaryFileFromLocalFile,
   getTestExecutionContext,
 } from '@jvalue/jayvee-execution/test';
-import { TabularLangExtension } from '@jvalue/jayvee-extensions/tabular/lang';
 import {
   BlockDefinition,
   IOType,
   createJayveeServices,
-  useExtension,
 } from '@jvalue/jayvee-language-server';
 import {
   ParseHelperOptions,
-  TestLangExtension,
   expectNoParserAndLexerErrors,
+  loadTestExtensions,
   parseHelper,
   readJvTestAssetHelper,
 } from '@jvalue/jayvee-language-server/test';
@@ -77,12 +75,12 @@ describe('Validation of XLSXInterpreterExecutor', () => {
     );
   }
 
-  beforeAll(() => {
-    // Register extensions
-    useExtension(new TabularLangExtension());
-    useExtension(new TestLangExtension());
+  beforeAll(async () => {
     // Create language services
     const services = createJayveeServices(NodeFileSystem).Jayvee;
+    await loadTestExtensions(services, [
+      path.resolve(__dirname, '../../test/test-extension/TestBlockTypes.jv'),
+    ]);
     locator = services.workspace.AstNodeLocator;
     // Parse function for Jayvee (without validation)
     parse = parseHelper(services);
diff --git a/libs/extensions/tabular/exec/test/test-extension/TestBlockTypes.jv b/libs/extensions/tabular/exec/test/test-extension/TestBlockTypes.jv
new file mode 100644
index 000000000..ba08556c4
--- /dev/null
+++ b/libs/extensions/tabular/exec/test/test-extension/TestBlockTypes.jv
@@ -0,0 +1,43 @@
+// SPDX-FileCopyrightText: 2023 Friedrich-Alexander-Universitat Erlangen-Nurnberg
+//
+// SPDX-License-Identifier: AGPL-3.0-only
+
+builtin blocktype TestSheetExtractor {
+    input inPort oftype None;
+    output outPort oftype Sheet;
+}
+
+builtin blocktype TestSheetLoader {
+    input inPort oftype Sheet;
+    output outPort oftype None;
+}
+
+builtin blocktype TestTextFileExtractor {
+    input inPort oftype None;
+    output outPort oftype TextFile;
+}
+
+builtin blocktype TestFileExtractor {
+    input inPort oftype None;
+    output outPort oftype File;
+}
+
+builtin blocktype TestWorkbookExtractor {
+    input inPort oftype None;
+    output outPort oftype Workbook;
+}
+
+builtin blocktype TestWorkbookLoader {
+    input inPort oftype Workbook;
+    output outPort oftype None;
+}
+
+builtin blocktype TestTableExtractor {
+    input inPort oftype None;
+    output outPort oftype Table;
+}
+
+builtin blocktype TestTableLoader {
+    input inPort oftype Table;
+    output outPort oftype None;
+}