Support casting types with expect statements

spec/features/expect_type_spec.cr

@@ -0,0 +1,36 @@
+require "../spec_helper"
+
+Spectator.describe "Expect Type" do
+  it "ensures a type is cast" do
+    value = 42.as(String | Int32)
+    expect(value).to be_a(String | Int32)
+    expect(value).to compile_as(String | Int32)
+    value = expect(value).to be_a(Int32)
+    expect(value).to eq(42)
+    expect(value).to be_a(Int32)
+    expect(value).to compile_as(Int32)
+    expect(value).to_not respond_to(:downcase)
+  end
+
+  it "ensures a type is not nil" do
+    value = 42.as(Int32?)
+    expect(value).to be_a(Int32?)
+    expect(value).to compile_as(Int32?)
+    value = expect(value).to_not be_nil
+    expect(value).to eq(42)
+    expect(value).to be_a(Int32)
+    expect(value).to compile_as(Int32)
+    expect { value.not_nil! }.to_not raise_error(NilAssertionError)
+  end
+
+  it "removes types from a union" do
+    value = 42.as(String | Int32)
+    expect(value).to be_a(String | Int32)
+    expect(value).to compile_as(String | Int32)
+    value = expect(value).to_not be_a(String)
+    expect(value).to eq(42)
+    expect(value).to be_a(Int32)
+    expect(value).to compile_as(Int32)
+    expect(value).to_not respond_to(:downcase)
+  end
+end