Added tests for operations that use assignable to/from.

tests/cases/conformance/types/stringLiteral/stringLiteralCheckedInIf01.ts

@@ -0,0 +1,17 @@
+
+type S = "a" | "b";
+type T = S[] | S;
+
+function f(foo: T) {
+    if (foo === "a") {
+        return foo;
+    }
+    else if (foo === "b") {
+        return foo;
+    }
+    else { 
+        return (foo as S[])[0];
+    }
+
+    throw new Error("Unreachable code hit.");
+}

tests/cases/conformance/types/stringLiteral/stringLiteralCheckedInIf02.ts

@@ -0,0 +1,18 @@
+
+type S = "a" | "b";
+type T = S[] | S;
+
+function isS(t: T): t is S {
+    return t === "a" || t === "b";
+}
+
+function f(foo: T) {
+    if (isS(foo)) {
+        return foo;
+    }
+    else { 
+        return foo[0];
+    }
+
+    throw new Error("Unreachable code hit.");
+}

tests/cases/conformance/types/stringLiteral/stringLiteralMatchedInSwitch01.ts

@@ -0,0 +1,13 @@
+
+type S = "a" | "b";
+type T = S[] | S;
+
+var foo: T;
+switch (foo) {
+    case "a":
+    case "b":
+        break;
+    default:
+        foo = (foo as S[])[0];
+        break;
+}

tests/cases/conformance/types/stringLiteral/stringLiteralTypeAssertion01.ts

@@ -0,0 +1,31 @@
+
+type S = "a" | "b";
+type T = S[] | S;
+
+var s: S;
+var t: T;
+var str: string;
+
+////////////////
+
+s = <S>t;
+s = t as S;
+
+s = <S>str;
+s = str as S;
+
+////////////////
+
+t = <T>s;
+t = s as T;
+
+t = <T>str;
+t = str as T;
+
+////////////////
+
+str = <string>s;
+str = s as string;
+
+str = <string>t;
+str = t as string;