Added test.

tests/cases/compiler/errorsOnWeakTypeIntersectionTargets01.ts

@@ -0,0 +1,40 @@
+interface A {
+    a: number;
+}
+
+interface B {
+    b?: string;
+}
+
+// 'b' is incompatible.
+export let x1: A & B = {
+    a: 0,
+    b: 12,
+}
+
+// 'a' is incompatible, 'b' is present and compatible.
+export let x2: A & B = {
+    a: "hello",
+    b: "hello",
+}
+
+// 'a' is incompatible, 'b' is absent.
+export let x3: A & B = {
+    a: "hello",
+}
+
+// Both 'a' and 'b' are incompatible
+export let x4: A & B = {
+    a: "hello",
+    b: 0,
+}
+
+// 'b' is compatible, 'a' is missing
+export let x5: A & B = {
+    b: 0,
+}
+
+// 'b' is incompatible, 'a' is missing
+export let x6: A & B = {
+    b: "",
+}