Add edge tests around Provide and Invoke

dig_test.go

@@ -247,7 +247,27 @@ func TestEndToEndSuccess(t *testing.T) {
 		require.NoError(t, c.Invoke(func(a *A, b *B) {}), "AB invoke failed")
 		require.Equal(t, 1, count, "Constructor must be called once")
 	})
+	t.Run("method invocation inside Invoke", func(t *testing.T) {
+		c := New()
+		type A struct{}
+		type B struct{}
+		cA := func() (*A, error) {
+			return &A{}, nil
+		}
+		cB := func() (*B, error) {
+			return &B{}, nil
+		}
+		getA := func(a *A) {
+			c.Invoke(func(b *B) {
+				assert.NotNil(t, b, "got nil B")
+			})
+			assert.NotNil(t, a, "got nil A")
+		}
 
+		require.NoError(t, c.Provide(cA), "provide failed")
+		require.NoError(t, c.Provide(cB), "provide failed")
+		require.NoError(t, c.Invoke(getA), "A invoke failed")
+	})
 	t.Run("collections and instances of same type", func(t *testing.T) {
 		c := New()
 		require.NoError(t, c.Provide(func() []*bytes.Buffer {
@@ -259,6 +279,17 @@ func TestEndToEndSuccess(t *testing.T) {
 	})
 }
 
+func TestProvideConstructorErrors(t *testing.T) {
+	t.Run("multiple-type constructor returns multiple objects of same type", func(t *testing.T) {
+		c := New()
+		type A struct{}
+		constructor := func() (*A, *A, error) {
+			return &A{}, &A{}, nil
+		}
+		require.Error(t, c.Provide(constructor), "provide failed")
+	})
+}
+
 func TestProvideRespectsConstructorErrors(t *testing.T) {
 	t.Run("constructor succeeds", func(t *testing.T) {
 		c := New()
@@ -349,6 +380,21 @@ func TestProvideKnownTypesFails(t *testing.T) {
 
 		})
 	}
+	t.Run("provide constructor twice", func(t *testing.T) {
+		c := New()
+		assert.NoError(t, c.Provide(func() *bytes.Buffer { return nil }))
+		assert.Error(t, c.Provide(func() *bytes.Buffer { return nil }))
+	})
+	t.Run("provide instance and constructor fails", func(t *testing.T) {
+		c := New()
+		assert.NoError(t, c.Provide(&bytes.Buffer{}))
+		assert.Error(t, c.Provide(func() *bytes.Buffer { return nil }))
+	})
+	t.Run("provide constructor then object instance fails", func(t *testing.T) {
+		c := New()
+		assert.NoError(t, c.Provide(func() *bytes.Buffer { return nil }))
+		assert.Error(t, c.Provide(&bytes.Buffer{}))
+	})
 }
 
 func TestProvideCycleFails(t *testing.T) {