diff --git a/assembler/test/test_021_parsing_failures.py b/assembler/test/test_021_parsing_failures.py
new file mode 100644
index 0000000..3a64168
--- /dev/null
+++ b/assembler/test/test_021_parsing_failures.py
@@ -0,0 +1,210 @@
+from io import StringIO
+import pytest
+
+from assembler.assembler import Assembler, ParsingError
+
+def test_missing_comma(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0 0xfe
+		ldi r1, 0xfe
+		add r0, r1
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+
+	with pytest.raises(ParsingError):
+		assembler.parse()
+
+def test_missing_newline(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0, 0xfe ldi r1, 0xfe
+		add r0, r1
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+
+	with pytest.raises(ParsingError):
+		assembler.parse()
+
+
+
+def test_additional_comma1(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi, r0, 0xfe 
+		ldi r1, 0xfe
+		add r0, r1
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+
+	with pytest.raises(ParsingError):
+		assembler.parse()
+
+def test_additional_comma2(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0, 0xfe,
+		ldi r1, 0xfe
+		add r0, r1
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+
+	with pytest.raises(ParsingError):
+		assembler.parse()
+
+
+
+def test_bad_mark1(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0, 0xfe
+		this_is_a_bad_mark
+		ldi r1, 0xfe
+		add r0, r1
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+
+	with pytest.raises(ParsingError):
+		assembler.parse()
+
+def test_bad_mark2(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0, 0xfe
+		This_is_a_bad_mark:
+		ldi r1, 0xfe
+		add r0, r1
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+
+	with pytest.raises(ParsingError):
+		assembler.parse()
+
+def test_bad_mark3(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0, 0xfe
+		0this_is_a_bad_mark:
+		ldi r1, 0xfe
+		add r0, r1
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+
+	with pytest.raises(ParsingError):
+		assembler.parse()
+
+def test_bad_mark4(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0, this_is_a_missing_mark
+		ldi r1, 0xfe
+		add r0, r1
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+
+	with pytest.raises(ParsingError):
+		assembler.parse()
+
+def test_bad_mark5(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0, this_is_a_missing_mark:
+		ldi r1, 0xfe
+		add r0, r1
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+
+	with pytest.raises(ParsingError):
+		assembler.parse()
+
+def test_bad_directive1(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0, 0
+		ldi r1, 0xfe
+		add r0, r1
+		.set data [0x00, 0x10]
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+
+	with pytest.raises(ParsingError):
+		assembler.parse()
+
+def test_bad_directive2(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0, 0
+		ldi r1, 0xfe
+		add r0, r1
+		.set[0x00, 0x10]
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+
+	with pytest.raises(ParsingError):
+		assembler.parse()
+
+def test_bad_directive3(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0, 0
+		ldi r1, 0xfe
+		add r0, r1
+		.set [0x00, 0x10,]
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+
+	with pytest.raises(ParsingError):
+		assembler.parse()
+
+def test_bad_directive4(basic_machine_definition):
+	memory_definition, command_defintion = basic_machine_definition
+
+	data = StringIO(
+		'''
+		ldi r0, 0
+		ldi r1, 0xfe
+		add r0, r1
+		.set [0x00, 0x10
+		'''
+		)
+	assembler = Assembler(data, memory_definition, command_defintion, {})
+
+	with pytest.raises(ParsingError):
+		assembler.parse()
+