diff --git a/tests/cases/checker/01_simple_types.py b/tests/cases/checker/01_simple_types.py
new file mode 100644
index 0000000..3566f9a
--- /dev/null
+++ b/tests/cases/checker/01_simple_types.py
@@ -0,0 +1,14 @@
+# type: ignore
+# ruff: disable[F821]
+from __future__ import annotations
+
+df: Frame[
+    verified: bool,
+    birth_year: int,
+    height: float + ( _ > 0 ) + ( _ < 250 ),
+    name: str,
+    date: datetime,
+    float,
+    unknown: _,
+    _
+]
diff --git a/tests/cases/checker/01_simple_types.py.ref.json b/tests/cases/checker/01_simple_types.py.ref.json
new file mode 100644
index 0000000..c37fb01
--- /dev/null
+++ b/tests/cases/checker/01_simple_types.py.ref.json
@@ -0,0 +1,3 @@
+{
+  "diagnostics": []
+}
\ No newline at end of file
diff --git a/tests/cases/checker/02_simple_operations.py b/tests/cases/checker/02_simple_operations.py
new file mode 100644
index 0000000..9e936c1
--- /dev/null
+++ b/tests/cases/checker/02_simple_operations.py
@@ -0,0 +1,11 @@
+a: int = 3
+b: int = 4
+
+c = a + b
+
+c = "invalid"
+
+d = True
+e = d + d
+
+f: float = a
diff --git a/tests/cases/checker/02_simple_operations.py.ref.json b/tests/cases/checker/02_simple_operations.py.ref.json
new file mode 100644
index 0000000..c390e27
--- /dev/null
+++ b/tests/cases/checker/02_simple_operations.py.ref.json
@@ -0,0 +1,46 @@
+{
+  "diagnostics": [
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          6,
+          0
+        ],
+        "end": [
+          6,
+          13
+        ]
+      },
+      "message": "Cannot assign BaseType(name='str') to c of type BaseType(name='int')"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          9,
+          4
+        ],
+        "end": [
+          9,
+          9
+        ]
+      },
+      "message": "Undefined operation __add__ between BaseType(name='bool') and BaseType(name='bool')"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          11,
+          0
+        ],
+        "end": [
+          11,
+          12
+        ]
+      },
+      "message": "Cannot assign BaseType(name='int') to f of type BaseType(name='float')"
+    }
+  ]
+}
\ No newline at end of file
diff --git a/tests/cases/checker/03_functions.py b/tests/cases/checker/03_functions.py
new file mode 100644
index 0000000..ddc0a56
--- /dev/null
+++ b/tests/cases/checker/03_functions.py
@@ -0,0 +1,18 @@
+def foo(a: int, /, b: float, *, c: str):
+    return True
+
+
+r1 = foo()
+r2 = foo(1)
+r3 = foo(1, 2.0)
+r4 = foo(1, b=2.0)
+r5 = foo(1, 2.0, "test")
+r6 = foo(1, 2.0, b=3.0)
+r7 = foo(a=1)
+r8 = foo(g="test")
+
+r9a = foo(1, 2.0, c="test")
+r9b = foo(1, b=2.0, c="test")
+r9c = foo(1, c="test", b=2.0)
+
+r10 = foo("a", 3, c=False)
diff --git a/tests/cases/checker/03_functions.py.ref.json b/tests/cases/checker/03_functions.py.ref.json
new file mode 100644
index 0000000..40b33b5
--- /dev/null
+++ b/tests/cases/checker/03_functions.py.ref.json
@@ -0,0 +1,270 @@
+{
+  "diagnostics": [
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          5,
+          5
+        ],
+        "end": [
+          5,
+          10
+        ]
+      },
+      "message": "Missing required positional arguments: 'a' and 'b'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          5,
+          5
+        ],
+        "end": [
+          5,
+          10
+        ]
+      },
+      "message": "Missing required keyword argument: 'c'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          6,
+          5
+        ],
+        "end": [
+          6,
+          11
+        ]
+      },
+      "message": "Missing required positional argument: 'b'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          6,
+          5
+        ],
+        "end": [
+          6,
+          11
+        ]
+      },
+      "message": "Missing required keyword argument: 'c'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          7,
+          5
+        ],
+        "end": [
+          7,
+          16
+        ]
+      },
+      "message": "Missing required keyword argument: 'c'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          8,
+          5
+        ],
+        "end": [
+          8,
+          18
+        ]
+      },
+      "message": "Missing required keyword argument: 'c'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          9,
+          17
+        ],
+        "end": [
+          9,
+          23
+        ]
+      },
+      "message": "Too many positional arguments"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          9,
+          5
+        ],
+        "end": [
+          9,
+          24
+        ]
+      },
+      "message": "Missing required keyword argument: 'c'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          10,
+          19
+        ],
+        "end": [
+          10,
+          22
+        ]
+      },
+      "message": "Multiple values for argument 'b'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          10,
+          5
+        ],
+        "end": [
+          10,
+          23
+        ]
+      },
+      "message": "Missing required keyword argument: 'c'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          11,
+          11
+        ],
+        "end": [
+          11,
+          12
+        ]
+      },
+      "message": "Unknown keyword argument 'a'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          11,
+          5
+        ],
+        "end": [
+          11,
+          13
+        ]
+      },
+      "message": "Missing required positional arguments: 'a' and 'b'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          11,
+          5
+        ],
+        "end": [
+          11,
+          13
+        ]
+      },
+      "message": "Missing required keyword argument: 'c'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          12,
+          11
+        ],
+        "end": [
+          12,
+          17
+        ]
+      },
+      "message": "Unknown keyword argument 'g'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          12,
+          5
+        ],
+        "end": [
+          12,
+          18
+        ]
+      },
+      "message": "Missing required positional arguments: 'a' and 'b'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          12,
+          5
+        ],
+        "end": [
+          12,
+          18
+        ]
+      },
+      "message": "Missing required keyword argument: 'c'"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          18,
+          10
+        ],
+        "end": [
+          18,
+          13
+        ]
+      },
+      "message": "Wrong type for argument 'a', expected BaseType(name='int'), got BaseType(name='str')"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          18,
+          15
+        ],
+        "end": [
+          18,
+          16
+        ]
+      },
+      "message": "Wrong type for argument 'b', expected BaseType(name='float'), got BaseType(name='int')"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          18,
+          20
+        ],
+        "end": [
+          18,
+          25
+        ]
+      },
+      "message": "Wrong type for argument 'c', expected BaseType(name='str'), got BaseType(name='bool')"
+    }
+  ]
+}
\ No newline at end of file
diff --git a/tests/cases/checker/04_custom_types.midas b/tests/cases/checker/04_custom_types.midas
new file mode 100644
index 0000000..eee3eb9
--- /dev/null
+++ b/tests/cases/checker/04_custom_types.midas
@@ -0,0 +1,14 @@
+type Meter(float)
+type Second(float)
+type MeterPerSecond(float)
+
+extend Meter {
+    op __add__(Meter) -> Meter
+    op __sub__(Meter) -> Meter
+    op __truediv__(Second) -> MeterPerSecond
+}
+
+extend Second {
+    op __add__(Second) -> Second
+    op __sub__(Second) -> Second
+}
diff --git a/tests/cases/checker/04_custom_types.py b/tests/cases/checker/04_custom_types.py
new file mode 100644
index 0000000..d176181
--- /dev/null
+++ b/tests/cases/checker/04_custom_types.py
@@ -0,0 +1,8 @@
+# type: ignore
+# ruff: disable [F821]
+
+midas.using("04_custom_types.midas")
+
+distance: Meter = 123.45
+time: Second = 6.7
+speed = distance / time
diff --git a/tests/cases/checker/04_custom_types.py.ref.json b/tests/cases/checker/04_custom_types.py.ref.json
new file mode 100644
index 0000000..de13745
--- /dev/null
+++ b/tests/cases/checker/04_custom_types.py.ref.json
@@ -0,0 +1,32 @@
+{
+  "diagnostics": [
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          6,
+          0
+        ],
+        "end": [
+          6,
+          24
+        ]
+      },
+      "message": "Cannot assign BaseType(name='float') to distance of type SimpleType(name='Meter', base=BaseType(name='float'))"
+    },
+    {
+      "type": "Error",
+      "location": {
+        "start": [
+          7,
+          0
+        ],
+        "end": [
+          7,
+          18
+        ]
+      },
+      "message": "Cannot assign BaseType(name='float') to time of type SimpleType(name='Second', base=BaseType(name='float'))"
+    }
+  ]
+}
\ No newline at end of file