diff --git a/test/unit/util/define-dynamic-block.test.js b/test/unit/util/define-dynamic-block.test.js
new file mode 100644
index 0000000000000000000000000000000000000000..655c054234c0be3b90e1a6854ad5feb5c7ecab39
--- /dev/null
+++ b/test/unit/util/define-dynamic-block.test.js
@@ -0,0 +1,203 @@
+import defineDynamicBlock from '../../../src/lib/define-dynamic-block';
+
+import ArgumentType from 'scratch-vm/src/extension-support/argument-type';
+import BlockType from 'scratch-vm/src/extension-support/block-type';
+
+const MockScratchBlocks = {
+    OUTPUT_SHAPE_HEXAGONAL: 1,
+    OUTPUT_SHAPE_ROUND: 2,
+    OUTPUT_SHAPE_SQUARE: 3
+};
+
+const categoryInfo = {
+    name: 'test category',
+    color1: '#111',
+    color2: '#222',
+    color3: '#333'
+};
+
+const penIconURI = 'data:image/svg+xml;base64,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';
+
+const testBlockInfo = {
+    commandWithIcon: {
+        blockType: BlockType.COMMAND,
+        blockIconURI: penIconURI,
+        text: 'command with icon'
+    },
+    commandWithoutIcon: {
+        blockType: BlockType.COMMAND,
+        text: 'command without icon'
+    },
+    terminalCommand: {
+        blockType: BlockType.COMMAND,
+        isTerminal: true,
+        text: 'terminal command'
+    },
+    reporter: {
+        blockType: BlockType.REPORTER,
+        text: 'reporter'
+    },
+    boolean: {
+        blockType: BlockType.BOOLEAN,
+        text: 'Boolean'
+    },
+    hat: {
+        blockType: BlockType.HAT,
+        text: 'hat'
+    }
+};
+
+// similar to goog.mixin from the Closure library
+const mixin = function (target, source) {
+    for (const x in source) {
+        target[x] = source[x];
+    }
+};
+
+class MockBlock {
+    // mocks the Blockly.Block constructor
+    static create (blockInfo, extendedOpcode) {
+        // mock the Blockly.Block constructor
+        const block = new MockBlock();
+        const prototype = defineDynamicBlock(MockScratchBlocks, categoryInfo, blockInfo, extendedOpcode);
+        mixin(block, prototype);
+        block.init();
+
+        // bootstrap the mutation<->DOM cycle
+        block.blockInfoText = JSON.stringify(blockInfo);
+        const xmlElement = block.mutationToDom();
+
+        // parse blockInfo from XML to fill dynamic properties
+        block.domToMutation(xmlElement);
+
+        return block;
+    }
+
+    jsonInit (json) {
+        this.result = Object.assign({}, json);
+    }
+    interpolate_ () {
+        // TODO: add tests for this?
+    }
+    setCheckboxInFlyout (isEnabled) {
+        this.result.checkboxInFlyout_ = isEnabled;
+    }
+    setOutput (isEnabled) {
+        this.result.outputConnection = isEnabled; // Blockly calls `makeConnection_` here
+    }
+    setOutputShape (outputShape) {
+        this.result.outputShape_ = outputShape;
+    }
+    setNextStatement (isEnabled) {
+        this.result.nextConnection = isEnabled; // Blockly calls `makeConnection_` here
+    }
+    setPreviousStatement (isEnabled) {
+        this.result.previousConnection = isEnabled; // Blockly calls `makeConnection_` here
+    }
+}
+
+describe('defineDynamicBlock', () => {
+    test('is a function', () => {
+        expect(typeof defineDynamicBlock).toBe('function');
+    });
+    test('can define a command block with an icon', () => {
+        const extendedOpcode = 'test.commandWithIcon';
+        const block = MockBlock.create(testBlockInfo.commandWithIcon, extendedOpcode);
+        expect(block.result).toEqual({
+            category: categoryInfo.name,
+            colour: categoryInfo.color1,
+            colourSecondary: categoryInfo.color2,
+            colourTertiary: categoryInfo.color3,
+            extensions: ['scratch_extension'],
+            inputsInline: true,
+            nextConnection: true,
+            outputShape_: MockScratchBlocks.OUTPUT_SHAPE_SQUARE,
+            previousConnection: true,
+            type: extendedOpcode
+        });
+    });
+    test('can define a command block without an icon', () => {
+        const extendedOpcode = 'test.commandWithoutIcon';
+        const block = MockBlock.create(testBlockInfo.commandWithoutIcon, extendedOpcode);
+        expect(block.result).toEqual({
+            category: categoryInfo.name,
+            colour: categoryInfo.color1,
+            colourSecondary: categoryInfo.color2,
+            colourTertiary: categoryInfo.color3,
+            // extensions: undefined, // no icon means no extension
+            inputsInline: true,
+            nextConnection: true,
+            outputShape_: MockScratchBlocks.OUTPUT_SHAPE_SQUARE,
+            previousConnection: true,
+            type: extendedOpcode
+        });
+    });
+    test('can define a terminal command', () => {
+        const extendedOpcode = 'test.terminal';
+        const block = MockBlock.create(testBlockInfo.terminalCommand, extendedOpcode);
+        expect(block.result).toEqual({
+            category: categoryInfo.name,
+            colour: categoryInfo.color1,
+            colourSecondary: categoryInfo.color2,
+            colourTertiary: categoryInfo.color3,
+            // extensions: undefined, // no icon means no extension
+            inputsInline: true,
+            nextConnection: false, // terminal
+            outputShape_: MockScratchBlocks.OUTPUT_SHAPE_SQUARE,
+            previousConnection: true,
+            type: extendedOpcode
+        });
+    });
+    test('can define a reporter', () => {
+        const extendedOpcode = 'test.reporter';
+        const block = MockBlock.create(testBlockInfo.reporter, extendedOpcode);
+        expect(block.result).toEqual({
+            category: categoryInfo.name,
+            checkboxInFlyout_: true,
+            colour: categoryInfo.color1,
+            colourSecondary: categoryInfo.color2,
+            colourTertiary: categoryInfo.color3,
+            // extensions: undefined, // no icon means no extension
+            inputsInline: true,
+            // nextConnection: undefined, // reporter
+            outputConnection: true, // reporter
+            outputShape_: MockScratchBlocks.OUTPUT_SHAPE_ROUND, // reporter
+            // previousConnection: undefined, // reporter
+            type: extendedOpcode
+        });
+    });
+    test('can define a Boolean', () => {
+        const extendedOpcode = 'test.boolean';
+        const block = MockBlock.create(testBlockInfo.boolean, extendedOpcode);
+        expect(block.result).toEqual({
+            category: categoryInfo.name,
+            // checkboxInFlyout_: undefined,
+            colour: categoryInfo.color1,
+            colourSecondary: categoryInfo.color2,
+            colourTertiary: categoryInfo.color3,
+            // extensions: undefined, // no icon means no extension
+            inputsInline: true,
+            // nextConnection: undefined, // reporter
+            outputConnection: true, // reporter
+            outputShape_: MockScratchBlocks.OUTPUT_SHAPE_HEXAGONAL, // Boolean
+            // previousConnection: undefined, // reporter
+            type: extendedOpcode
+        });
+    });
+    test('can define a hat', () => {
+        const extendedOpcode = 'test.hat';
+        const block = MockBlock.create(testBlockInfo.hat, extendedOpcode);
+        expect(block.result).toEqual({
+            category: categoryInfo.name,
+            colour: categoryInfo.color1,
+            colourSecondary: categoryInfo.color2,
+            colourTertiary: categoryInfo.color3,
+            // extensions: undefined, // no icon means no extension
+            inputsInline: true,
+            nextConnection: true,
+            outputShape_: MockScratchBlocks.OUTPUT_SHAPE_SQUARE,
+            // previousConnection: undefined, // hat
+            type: extendedOpcode
+        });
+    });
+});