Swift: Add a test for assignment exprs.

swift/ql/test/library-tests/elements/expr/assignment/assignment.expected

@@ -0,0 +1,2 @@
+| assignment.swift:6:2:6:6 |  ... = ... | AssignExpr | x | 1 |
+| assignment.swift:33:2:33:6 |  ... = ... | AssignExpr | y | z |

swift/ql/test/library-tests/elements/expr/assignment/assignment.ql

@@ -0,0 +1,14 @@
+import swift
+
+string describe(Expr e) {
+  e instanceof AssignExpr and result = "AssignExpr"
+}
+
+from AssignExpr e
+where
+  e.getLocation().getFile().getBaseName() != ""
+select
+  e,
+  concat(describe(e), ", "),
+  concat(e.getDest().toString(), ", "),
+  concat(e.getSource().toString(), ", ")

swift/ql/test/library-tests/elements/expr/assignment/assignment.swift

@@ -0,0 +1,37 @@
+
+func test() {
+	var x = 0
+
+	// simple assignment
+	x = 1
+
+	// arithmetic assignment operations
+	x += 1
+	x -= 1
+	x *= 1
+	x /= 1
+	x %= 1
+
+	// bitwise assignment operations
+	x &= 1
+	x |= 1
+	x ^= 1
+	x <<= 1
+	x >>= 1
+
+	// assignment operations with overflow
+	x &*= 1
+	x &+= 1
+	x &-= 1
+	x &<<= 1
+	x &>>= 1
+
+	// pointwise assignment operations
+	var y = SIMD4<Int>(1, 2, 3, 4)
+	let z = SIMD4<Int>(5, 6, 7, 8)
+	var m = y .< z
+	y = z
+	m .&= m
+	m .|= m
+	m .^= m
+}